<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:bc31ed0b-ee00-456b-a007-12251f5174cb,g:81905d62-be14-4bd9-ba09-a863dc1b6c92-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.westpharma.com/role/RevenueRevenueRecognitionDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#RevenueRevenueRecognitionDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/RevenueRevenueRecognitionDetails" xlink:type="extended" id="i7bad45d783ba43ea88b4417cfd187044_RevenueRevenueRecognitionDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_ad505586-cbba-47b6-bd66-16ecb066d125" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_4a81a7ed-edc7-4c4e-bc6f-dd3c53b32665" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_ad505586-cbba-47b6-bd66-16ecb066d125" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_4a81a7ed-edc7-4c4e-bc6f-dd3c53b32665" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_a3652f1a-07d9-4387-ab5b-a1ab8a761706" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_ad505586-cbba-47b6-bd66-16ecb066d125" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_a3652f1a-07d9-4387-ab5b-a1ab8a761706" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_de55741a-3c39-4af6-bae5-d302d8e1e7a2" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a3652f1a-07d9-4387-ab5b-a1ab8a761706" xlink:to="loc_srt_MajorCustomersAxis_de55741a-3c39-4af6-bae5-d302d8e1e7a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_de55741a-3c39-4af6-bae5-d302d8e1e7a2_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_de55741a-3c39-4af6-bae5-d302d8e1e7a2" xlink:to="loc_srt_NameOfMajorCustomerDomain_de55741a-3c39-4af6-bae5-d302d8e1e7a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_7d9587db-a19b-4dd1-8bb2-6e18e4d20db2" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_de55741a-3c39-4af6-bae5-d302d8e1e7a2" xlink:to="loc_srt_NameOfMajorCustomerDomain_7d9587db-a19b-4dd1-8bb2-6e18e4d20db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_BiologicsCustomersMember_1c4272ab-7fc8-484c-a57b-70181581c52e" xlink:href="wst-20220331.xsd#wst_BiologicsCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_7d9587db-a19b-4dd1-8bb2-6e18e4d20db2" xlink:to="loc_wst_BiologicsCustomersMember_1c4272ab-7fc8-484c-a57b-70181581c52e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_GenericsCustomersMember_b384754f-2642-472e-9376-5a0ca248fa48" xlink:href="wst-20220331.xsd#wst_GenericsCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_7d9587db-a19b-4dd1-8bb2-6e18e4d20db2" xlink:to="loc_wst_GenericsCustomersMember_b384754f-2642-472e-9376-5a0ca248fa48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_PharmaCustomersMember_a66f040d-8486-4c41-a17a-fdf5a6952bd1" xlink:href="wst-20220331.xsd#wst_PharmaCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_7d9587db-a19b-4dd1-8bb2-6e18e4d20db2" xlink:to="loc_wst_PharmaCustomersMember_a66f040d-8486-4c41-a17a-fdf5a6952bd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_ContractManufacturedCustomersMember_94d49722-c172-4991-8a6f-f7fb5c86fe5f" xlink:href="wst-20220331.xsd#wst_ContractManufacturedCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_7d9587db-a19b-4dd1-8bb2-6e18e4d20db2" xlink:to="loc_wst_ContractManufacturedCustomersMember_94d49722-c172-4991-8a6f-f7fb5c86fe5f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_a29c372a-4c60-4b19-b7d8-ac0c3f400931" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a3652f1a-07d9-4387-ab5b-a1ab8a761706" xlink:to="loc_srt_ProductOrServiceAxis_a29c372a-4c60-4b19-b7d8-ac0c3f400931" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a29c372a-4c60-4b19-b7d8-ac0c3f400931_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_a29c372a-4c60-4b19-b7d8-ac0c3f400931" xlink:to="loc_srt_ProductsAndServicesDomain_a29c372a-4c60-4b19-b7d8-ac0c3f400931_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_bbba8480-8eb9-41b2-8018-84a6008e1889" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_a29c372a-4c60-4b19-b7d8-ac0c3f400931" xlink:to="loc_srt_ProductsAndServicesDomain_bbba8480-8eb9-41b2-8018-84a6008e1889" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_HighValueProductComponentsMember_97961d69-005b-49fe-b318-5903c792dcb6" xlink:href="wst-20220331.xsd#wst_HighValueProductComponentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bbba8480-8eb9-41b2-8018-84a6008e1889" xlink:to="loc_wst_HighValueProductComponentsMember_97961d69-005b-49fe-b318-5903c792dcb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_HighValueProductDeliveryDevicesMember_04d29773-5fec-4d40-86a5-1f878595dc25" xlink:href="wst-20220331.xsd#wst_HighValueProductDeliveryDevicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bbba8480-8eb9-41b2-8018-84a6008e1889" xlink:to="loc_wst_HighValueProductDeliveryDevicesMember_04d29773-5fec-4d40-86a5-1f878595dc25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_StandardPackagingMember_fb8c7484-b0d5-4961-9932-25625dabd523" xlink:href="wst-20220331.xsd#wst_StandardPackagingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bbba8480-8eb9-41b2-8018-84a6008e1889" xlink:to="loc_wst_StandardPackagingMember_fb8c7484-b0d5-4961-9932-25625dabd523" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_ContractManufacturedProductsMember_afb3c1d8-0a7a-4d69-9028-704c06075812" xlink:href="wst-20220331.xsd#wst_ContractManufacturedProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bbba8480-8eb9-41b2-8018-84a6008e1889" xlink:to="loc_wst_ContractManufacturedProductsMember_afb3c1d8-0a7a-4d69-9028-704c06075812" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_ccd53b59-c8b0-4f79-959d-9009aa45fde0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a3652f1a-07d9-4387-ab5b-a1ab8a761706" xlink:to="loc_srt_StatementGeographicalAxis_ccd53b59-c8b0-4f79-959d-9009aa45fde0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_ccd53b59-c8b0-4f79-959d-9009aa45fde0_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_ccd53b59-c8b0-4f79-959d-9009aa45fde0" xlink:to="loc_srt_SegmentGeographicalDomain_ccd53b59-c8b0-4f79-959d-9009aa45fde0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_bd2811d1-4058-4855-91b4-219c7ef2670b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_ccd53b59-c8b0-4f79-959d-9009aa45fde0" xlink:to="loc_srt_SegmentGeographicalDomain_bd2811d1-4058-4855-91b4-219c7ef2670b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AmericasMember_dd009962-3fb3-470a-b2e6-5990c960a55b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AmericasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_bd2811d1-4058-4855-91b4-219c7ef2670b" xlink:to="loc_srt_AmericasMember_dd009962-3fb3-470a-b2e6-5990c960a55b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_74c7df4e-80ca-4e04-92fd-d06ce535f50e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_bd2811d1-4058-4855-91b4-219c7ef2670b" xlink:to="loc_us-gaap_EMEAMember_74c7df4e-80ca-4e04-92fd-d06ce535f50e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_1381f233-5e39-497e-b252-c9dc15df65d8" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_bd2811d1-4058-4855-91b4-219c7ef2670b" xlink:to="loc_srt_AsiaPacificMember_1381f233-5e39-497e-b252-c9dc15df65d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_27ba2143-1268-4a86-99e2-4bff683216c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a3652f1a-07d9-4387-ab5b-a1ab8a761706" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_27ba2143-1268-4a86-99e2-4bff683216c0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27ba2143-1268-4a86-99e2-4bff683216c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_27ba2143-1268-4a86-99e2-4bff683216c0" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27ba2143-1268-4a86-99e2-4bff683216c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_14ff2e0a-4a39-4f95-af4b-1b835bd64fea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_27ba2143-1268-4a86-99e2-4bff683216c0" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_14ff2e0a-4a39-4f95-af4b-1b835bd64fea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_22025e99-0b34-443d-8dca-9356c11ee146" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_14ff2e0a-4a39-4f95-af4b-1b835bd64fea" xlink:to="loc_us-gaap_SalesRevenueNetMember_22025e99-0b34-443d-8dca-9356c11ee146" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_3c791a49-3b2b-4385-b5e0-830adc0759c5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a3652f1a-07d9-4387-ab5b-a1ab8a761706" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_3c791a49-3b2b-4385-b5e0-830adc0759c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_3c791a49-3b2b-4385-b5e0-830adc0759c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_3c791a49-3b2b-4385-b5e0-830adc0759c5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_3c791a49-3b2b-4385-b5e0-830adc0759c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_0ac11ff0-85dd-4db4-8ec3-8760e66f0574" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_3c791a49-3b2b-4385-b5e0-830adc0759c5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_0ac11ff0-85dd-4db4-8ec3-8760e66f0574" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_9ebffd22-b654-4496-bc9c-cf12da0b0f3d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_0ac11ff0-85dd-4db4-8ec3-8760e66f0574" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_9ebffd22-b654-4496-bc9c-cf12da0b0f3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_a89b8e53-aebd-477f-a909-3adaedcd5f3a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_0ac11ff0-85dd-4db4-8ec3-8760e66f0574" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_a89b8e53-aebd-477f-a909-3adaedcd5f3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_3c9aaac3-62db-4756-85f3-a0bc5961b0c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_0ac11ff0-85dd-4db4-8ec3-8760e66f0574" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_3c9aaac3-62db-4756-85f3-a0bc5961b0c4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/RevenueContractsandLiabilitiesNarrativeDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#RevenueContractsandLiabilitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/RevenueContractsandLiabilitiesNarrativeDetails" xlink:type="extended" id="i730058c5ae7d43aa8b4ae238ad96e94e_RevenueContractsandLiabilitiesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_bad1e48a-f72d-4dfa-ac91-4edb94338e90" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_f052e68f-d817-4aa3-81c6-2c877cc5e31c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bad1e48a-f72d-4dfa-ac91-4edb94338e90" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_f052e68f-d817-4aa3-81c6-2c877cc5e31c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_61b634da-cd23-40d0-9b03-7ff0bb9d0804" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bad1e48a-f72d-4dfa-ac91-4edb94338e90" xlink:to="loc_us-gaap_ContractWithCustomerLiability_61b634da-cd23-40d0-9b03-7ff0bb9d0804" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_0a2e3c6a-73b3-45ed-a712-e24d81b8b24e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bad1e48a-f72d-4dfa-ac91-4edb94338e90" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_0a2e3c6a-73b3-45ed-a712-e24d81b8b24e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_4ef7da9b-2364-49f5-b185-9502948fe951" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bad1e48a-f72d-4dfa-ac91-4edb94338e90" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_4ef7da9b-2364-49f5-b185-9502948fe951" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_0df1b1d0-d8a4-48d2-bbe8-615069b25354" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bad1e48a-f72d-4dfa-ac91-4edb94338e90" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_0df1b1d0-d8a4-48d2-bbe8-615069b25354" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_aa35e056-b0b5-4a7e-9d54-3196cb539991" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_0df1b1d0-d8a4-48d2-bbe8-615069b25354" xlink:to="loc_srt_ProductOrServiceAxis_aa35e056-b0b5-4a7e-9d54-3196cb539991" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_aa35e056-b0b5-4a7e-9d54-3196cb539991_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_aa35e056-b0b5-4a7e-9d54-3196cb539991" xlink:to="loc_srt_ProductsAndServicesDomain_aa35e056-b0b5-4a7e-9d54-3196cb539991_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_30ea507f-9b4d-4d41-9cb8-3789ebb8931f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_aa35e056-b0b5-4a7e-9d54-3196cb539991" xlink:to="loc_srt_ProductsAndServicesDomain_30ea507f-9b4d-4d41-9cb8-3789ebb8931f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_SmartDoseMember_5e993bbe-b081-428e-bc9f-c4f675270f16" xlink:href="wst-20220331.xsd#wst_SmartDoseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_30ea507f-9b4d-4d41-9cb8-3789ebb8931f" xlink:to="loc_wst_SmartDoseMember_5e993bbe-b081-428e-bc9f-c4f675270f16" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/DebtLongtermDebtDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#DebtLongtermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/DebtLongtermDebtDetails" xlink:type="extended" id="ibe34c3a55ab54f32a111fa26773581b2_DebtLongtermDebtDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_e8e24943-89e4-4eca-84b7-01b221c2f9da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_e8e24943-89e4-4eca-84b7-01b221c2f9da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_c17f49a2-aa12-4330-8ceb-ca02259eacf9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_c17f49a2-aa12-4330-8ceb-ca02259eacf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_0cb52485-6403-4ca0-bf65-36cd97998c92" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_0cb52485-6403-4ca0-bf65-36cd97998c92" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_6a9c7b9c-4132-4714-a990-3a5c78f694fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:to="loc_us-gaap_LongTermDebt_6a9c7b9c-4132-4714-a990-3a5c78f694fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_13f14ab2-2bbb-44ac-9bbb-eb1bbe218a5d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:to="loc_us-gaap_LongTermDebtCurrent_13f14ab2-2bbb-44ac-9bbb-eb1bbe218a5d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_3ef8f06a-5a66-4d4e-8452-6b9cd1d2c925" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_3ef8f06a-5a66-4d4e-8452-6b9cd1d2c925" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_390e31c3-b5d4-481d-960e-61e5e9801632" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a1ec1e4a-95b0-4931-983b-124e30f2df7d" xlink:to="loc_us-gaap_DebtInstrumentTable_390e31c3-b5d4-481d-960e-61e5e9801632" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_643c7c6e-598f-42c8-bef0-0cc60fe8446d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_390e31c3-b5d4-481d-960e-61e5e9801632" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_643c7c6e-598f-42c8-bef0-0cc60fe8446d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_643c7c6e-598f-42c8-bef0-0cc60fe8446d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_643c7c6e-598f-42c8-bef0-0cc60fe8446d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_643c7c6e-598f-42c8-bef0-0cc60fe8446d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_435339a9-98ca-4752-bfe6-836b8e4c6714" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_643c7c6e-598f-42c8-bef0-0cc60fe8446d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_435339a9-98ca-4752-bfe6-836b8e4c6714" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_TermLoanDue2024Member_4d972fb7-b019-468a-ae00-f528718703e1" xlink:href="wst-20220331.xsd#wst_TermLoanDue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_435339a9-98ca-4752-bfe6-836b8e4c6714" xlink:to="loc_wst_TermLoanDue2024Member_4d972fb7-b019-468a-ae00-f528718703e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_SeniorNotesDue2022Member_f1428f97-1d4c-440a-a2ae-c31bfa49b817" xlink:href="wst-20220331.xsd#wst_SeniorNotesDue2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_435339a9-98ca-4752-bfe6-836b8e4c6714" xlink:to="loc_wst_SeniorNotesDue2022Member_f1428f97-1d4c-440a-a2ae-c31bfa49b817" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_SeniorBNotesDue2024Member_fd2bf248-b1ae-439c-a024-20e9ebcfc719" xlink:href="wst-20220331.xsd#wst_SeniorBNotesDue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_435339a9-98ca-4752-bfe6-836b8e4c6714" xlink:to="loc_wst_SeniorBNotesDue2024Member_fd2bf248-b1ae-439c-a024-20e9ebcfc719" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_SeniorCNotesDue2027Member_1f7ea7bc-5405-4c5d-b31a-72d753b42096" xlink:href="wst-20220331.xsd#wst_SeniorCNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_435339a9-98ca-4752-bfe6-836b8e4c6714" xlink:to="loc_wst_SeniorCNotesDue2027Member_1f7ea7bc-5405-4c5d-b31a-72d753b42096" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/DebtCreditFacilityDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#DebtCreditFacilityDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/DebtCreditFacilityDetails" xlink:type="extended" id="i016bd379e64246efb25b5db6cb01476f_DebtCreditFacilityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_54226264-c697-40d4-ab73-faeb34f1b7ed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_54226264-c697-40d4-ab73-faeb34f1b7ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_CreditFacilityIsAvailableForSwingLineLoans_b242304d-ea21-4d3a-bfdf-6aa186a4c215" xlink:href="wst-20220331.xsd#wst_CreditFacilityIsAvailableForSwingLineLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_wst_CreditFacilityIsAvailableForSwingLineLoans_b242304d-ea21-4d3a-bfdf-6aa186a4c215" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_CreditAvailableForIssuanceOfLettersOfCredit_7e6da2b0-5e8b-4cab-a93c-28885bb5efa9" xlink:href="wst-20220331.xsd#wst_CreditAvailableForIssuanceOfLettersOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_wst_CreditAvailableForIssuanceOfLettersOfCredit_7e6da2b0-5e8b-4cab-a93c-28885bb5efa9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_LineOfCreditFacilityAdditionalBorrowingCapacity_abb0078f-0329-46a4-80a8-36c5b2159e35" xlink:href="wst-20220331.xsd#wst_LineOfCreditFacilityAdditionalBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_wst_LineOfCreditFacilityAdditionalBorrowingCapacity_abb0078f-0329-46a4-80a8-36c5b2159e35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_DebtInstrumentIncreaseInFacilityPrecedingPeriod_5c26b33f-118d-47a2-97d5-31f878e415a4" xlink:href="wst-20220331.xsd#wst_DebtInstrumentIncreaseInFacilityPrecedingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_wst_DebtInstrumentIncreaseInFacilityPrecedingPeriod_5c26b33f-118d-47a2-97d5-31f878e415a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_487688b8-f0c8-4525-8b1d-82a923a1fb1f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_487688b8-f0c8-4525-8b1d-82a923a1fb1f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_DebtInstrumentRatioOfDebtToEBITDA_a6ae8fc9-a929-407c-8620-5c4a2cda0396" xlink:href="wst-20220331.xsd#wst_DebtInstrumentRatioOfDebtToEBITDA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_wst_DebtInstrumentRatioOfDebtToEBITDA_a6ae8fc9-a929-407c-8620-5c4a2cda0396" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_DebtInstrumentNumberOfInstancesRatioOfDebtToEBITDAExceeded_4b3c3f0a-9477-4750-b618-3b119d76b505" xlink:href="wst-20220331.xsd#wst_DebtInstrumentNumberOfInstancesRatioOfDebtToEBITDAExceeded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_wst_DebtInstrumentNumberOfInstancesRatioOfDebtToEBITDAExceeded_4b3c3f0a-9477-4750-b618-3b119d76b505" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_DebtInstrumentNumberOfFiscalQuartersFollowingAcquisition_99645f76-17f1-4097-b12d-bb0d364ae08b" xlink:href="wst-20220331.xsd#wst_DebtInstrumentNumberOfFiscalQuartersFollowingAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_wst_DebtInstrumentNumberOfFiscalQuartersFollowingAcquisition_99645f76-17f1-4097-b12d-bb0d364ae08b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_0aaec64e-c6fa-4c2a-bd94-dce5c8fe3b82" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_LineOfCredit_0aaec64e-c6fa-4c2a-bd94-dce5c8fe3b82" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_1ba1b988-1937-46c1-a3fa-724899dcd7e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_1ba1b988-1937-46c1-a3fa-724899dcd7e8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_b011d6d6-1363-4ffb-a211-022825df15fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_b011d6d6-1363-4ffb-a211-022825df15fd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_01f80691-469b-4d4c-a68e-51697538369e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_DebtCurrent_01f80691-469b-4d4c-a68e-51697538369e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_b6327f9d-e500-4feb-8518-e48ecc8a95b1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_b6327f9d-e500-4feb-8518-e48ecc8a95b1" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_dd6b9033-3dfc-4581-a718-bb92277de4e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_09fe29c4-09eb-467b-96ce-b4160bbb2417" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_dd6b9033-3dfc-4581-a718-bb92277de4e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_eade0106-601e-4b42-8fd7-45cd1f0f32b8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_dd6b9033-3dfc-4581-a718-bb92277de4e5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_eade0106-601e-4b42-8fd7-45cd1f0f32b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_eade0106-601e-4b42-8fd7-45cd1f0f32b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_eade0106-601e-4b42-8fd7-45cd1f0f32b8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_eade0106-601e-4b42-8fd7-45cd1f0f32b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_21d502ff-85f2-4a35-bc95-91fe0e6590a1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_eade0106-601e-4b42-8fd7-45cd1f0f32b8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_21d502ff-85f2-4a35-bc95-91fe0e6590a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_RevolvingCreditFacilityDue2024Member_93034f9f-3023-460c-ae75-ca4baaa973e9" xlink:href="wst-20220331.xsd#wst_RevolvingCreditFacilityDue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_21d502ff-85f2-4a35-bc95-91fe0e6590a1" xlink:to="loc_wst_RevolvingCreditFacilityDue2024Member_93034f9f-3023-460c-ae75-ca4baaa973e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_TermLoanDue2024Member_a9980a1c-977b-45ae-a26d-fd93b1dc678d" xlink:href="wst-20220331.xsd#wst_TermLoanDue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_21d502ff-85f2-4a35-bc95-91fe0e6590a1" xlink:to="loc_wst_TermLoanDue2024Member_a9980a1c-977b-45ae-a26d-fd93b1dc678d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_b2dd02c4-51d5-4613-9a2a-3f3629ca52d3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_dd6b9033-3dfc-4581-a718-bb92277de4e5" xlink:to="loc_us-gaap_CreditFacilityAxis_b2dd02c4-51d5-4613-9a2a-3f3629ca52d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_b2dd02c4-51d5-4613-9a2a-3f3629ca52d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_b2dd02c4-51d5-4613-9a2a-3f3629ca52d3" xlink:to="loc_us-gaap_CreditFacilityDomain_b2dd02c4-51d5-4613-9a2a-3f3629ca52d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_b2dd02c4-51d5-4613-9a2a-3f3629ca52d3" xlink:to="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticLineOfCreditMember_c63e62b6-2f87-4077-9ec7-8a5a2db9e699" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DomesticLineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:to="loc_us-gaap_DomesticLineOfCreditMember_c63e62b6-2f87-4077-9ec7-8a5a2db9e699" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignLineOfCreditMember_49d7ea0f-bdc2-4b11-bed6-3aa331d47be5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignLineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:to="loc_us-gaap_ForeignLineOfCreditMember_49d7ea0f-bdc2-4b11-bed6-3aa331d47be5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_b73df068-e33d-4ba3-8abc-e77af75637b3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_b73df068-e33d-4ba3-8abc-e77af75637b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_1652be37-3889-4479-8028-c9b43750e3ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_1652be37-3889-4479-8028-c9b43750e3ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_0e6a0283-f20a-4fb5-b36e-f374af66f67b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_0e6a0283-f20a-4fb5-b36e-f374af66f67b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_35c8d0fa-d8f7-4d84-ae57-55bfa0a13b4a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:to="loc_us-gaap_BaseRateMember_35c8d0fa-d8f7-4d84-ae57-55bfa0a13b4a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_9f5ad8a9-ae79-4d97-a34e-915bdfc67e65" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_014b4b51-d238-4550-94ba-faae233b727f" xlink:to="loc_us-gaap_LetterOfCreditMember_9f5ad8a9-ae79-4d97-a34e-915bdfc67e65" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_374ac6e1-c0a9-4d17-acde-f4e029573da7" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_dd6b9033-3dfc-4581-a718-bb92277de4e5" xlink:to="loc_srt_RangeAxis_374ac6e1-c0a9-4d17-acde-f4e029573da7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_374ac6e1-c0a9-4d17-acde-f4e029573da7_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_374ac6e1-c0a9-4d17-acde-f4e029573da7" xlink:to="loc_srt_RangeMember_374ac6e1-c0a9-4d17-acde-f4e029573da7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2be01c02-ca1d-4e71-a902-6d76e931af84" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_374ac6e1-c0a9-4d17-acde-f4e029573da7" xlink:to="loc_srt_RangeMember_2be01c02-ca1d-4e71-a902-6d76e931af84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_5c8f81f7-8023-42ed-b283-be37b32f4f33" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2be01c02-ca1d-4e71-a902-6d76e931af84" xlink:to="loc_srt_MinimumMember_5c8f81f7-8023-42ed-b283-be37b32f4f33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_39dec1fd-9944-425c-8cd2-e2f5b0816a88" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2be01c02-ca1d-4e71-a902-6d76e931af84" xlink:to="loc_srt_MaximumMember_39dec1fd-9944-425c-8cd2-e2f5b0816a88" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/DerivativeFinancialInstrumentsForeignExchangeRateRiskDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#DerivativeFinancialInstrumentsForeignExchangeRateRiskDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/DerivativeFinancialInstrumentsForeignExchangeRateRiskDetails" xlink:type="extended" id="i0c500e32403547a8883ad3126d8258df_DerivativeFinancialInstrumentsForeignExchangeRateRiskDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_819f14ea-cb27-484f-8201-48d1be9d3ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_92afadfd-80b4-43ad-bc8c-368c7e5b0382" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_819f14ea-cb27-484f-8201-48d1be9d3ae6" xlink:to="loc_us-gaap_DerivativeNotionalAmount_92afadfd-80b4-43ad-bc8c-368c7e5b0382" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTermOfContract_35a968ff-273b-47b1-9e0c-2abad317799b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_819f14ea-cb27-484f-8201-48d1be9d3ae6" xlink:to="loc_us-gaap_DerivativeTermOfContract_35a968ff-273b-47b1-9e0c-2abad317799b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNonmonetaryNotionalAmountVolume_09b7148b-2b4f-4bc6-8d4a-d9cec8d815b9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeNonmonetaryNotionalAmountVolume"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_819f14ea-cb27-484f-8201-48d1be9d3ae6" xlink:to="loc_us-gaap_DerivativeNonmonetaryNotionalAmountVolume_09b7148b-2b4f-4bc6-8d4a-d9cec8d815b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAveragePriceRiskOptionStrikePrice_fa50d1f9-875b-4cc6-a6cb-48357a3ffd52" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeAveragePriceRiskOptionStrikePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_819f14ea-cb27-484f-8201-48d1be9d3ae6" xlink:to="loc_us-gaap_DerivativeAveragePriceRiskOptionStrikePrice_fa50d1f9-875b-4cc6-a6cb-48357a3ffd52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_47fc99d0-349f-4e7a-95e5-58772c86d657" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_819f14ea-cb27-484f-8201-48d1be9d3ae6" xlink:to="loc_us-gaap_DerivativeTable_47fc99d0-349f-4e7a-95e5-58772c86d657" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_89106bdf-9ce3-48fd-9329-8c61ae481044" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_47fc99d0-349f-4e7a-95e5-58772c86d657" xlink:to="loc_srt_CurrencyAxis_89106bdf-9ce3-48fd-9329-8c61ae481044" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_89106bdf-9ce3-48fd-9329-8c61ae481044_default" xlink:href="https://xbrl.sec.gov/currency/2021/currency-2021.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_89106bdf-9ce3-48fd-9329-8c61ae481044" xlink:to="loc_currency_AllCurrenciesDomain_89106bdf-9ce3-48fd-9329-8c61ae481044_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_3077551c-c8f2-4170-8dda-47202ac232f2" xlink:href="https://xbrl.sec.gov/currency/2021/currency-2021.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_89106bdf-9ce3-48fd-9329-8c61ae481044" xlink:to="loc_currency_AllCurrenciesDomain_3077551c-c8f2-4170-8dda-47202ac232f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_bbba54ee-8974-4c72-ae7d-b6f0e50da6b2" xlink:href="https://xbrl.sec.gov/currency/2021/currency-2021.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_3077551c-c8f2-4170-8dda-47202ac232f2" xlink:to="loc_currency_USD_bbba54ee-8974-4c72-ae7d-b6f0e50da6b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_JPY_d9c74f9e-f8c7-4c48-9281-c3c15eda8d08" xlink:href="https://xbrl.sec.gov/currency/2021/currency-2021.xsd#currency_JPY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_3077551c-c8f2-4170-8dda-47202ac232f2" xlink:to="loc_currency_JPY_d9c74f9e-f8c7-4c48-9281-c3c15eda8d08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_SGD_1df72e8d-b25b-478d-be67-4b8f2ada22ff" xlink:href="https://xbrl.sec.gov/currency/2021/currency-2021.xsd#currency_SGD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_3077551c-c8f2-4170-8dda-47202ac232f2" xlink:to="loc_currency_SGD_1df72e8d-b25b-478d-be67-4b8f2ada22ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_e3f4ff3c-1dfc-4cab-a33c-205fdc713e3e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_47fc99d0-349f-4e7a-95e5-58772c86d657" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_e3f4ff3c-1dfc-4cab-a33c-205fdc713e3e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_e3f4ff3c-1dfc-4cab-a33c-205fdc713e3e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_e3f4ff3c-1dfc-4cab-a33c-205fdc713e3e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_e3f4ff3c-1dfc-4cab-a33c-205fdc713e3e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_25bfa85c-bfca-4b6f-93e7-215549e74553" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_e3f4ff3c-1dfc-4cab-a33c-205fdc713e3e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_25bfa85c-bfca-4b6f-93e7-215549e74553" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_2fbbe0f6-015a-4c15-812c-90b7f054c7f8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_25bfa85c-bfca-4b6f-93e7-215549e74553" xlink:to="loc_us-gaap_ForwardContractsMember_2fbbe0f6-015a-4c15-812c-90b7f054c7f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_c438fdfb-16d7-4d26-83a4-c2b067024179" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_25bfa85c-bfca-4b6f-93e7-215549e74553" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_c438fdfb-16d7-4d26-83a4-c2b067024179" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_4e14ae06-7f23-4f98-a455-b69edf2b48dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_25bfa85c-bfca-4b6f-93e7-215549e74553" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_4e14ae06-7f23-4f98-a455-b69edf2b48dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionMember_4f8afa08-daf3-43e0-91b3-243dadcc0b2f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_25bfa85c-bfca-4b6f-93e7-215549e74553" xlink:to="loc_us-gaap_OptionMember_4f8afa08-daf3-43e0-91b3-243dadcc0b2f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionAxis_e01f58f9-5352-43b2-8425-69ee2d3b0823" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PositionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_47fc99d0-349f-4e7a-95e5-58772c86d657" xlink:to="loc_us-gaap_PositionAxis_e01f58f9-5352-43b2-8425-69ee2d3b0823" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionDomain_e01f58f9-5352-43b2-8425-69ee2d3b0823_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PositionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PositionAxis_e01f58f9-5352-43b2-8425-69ee2d3b0823" xlink:to="loc_us-gaap_PositionDomain_e01f58f9-5352-43b2-8425-69ee2d3b0823_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionDomain_666eff44-9f98-444e-b32c-646967a6311b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PositionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PositionAxis_e01f58f9-5352-43b2-8425-69ee2d3b0823" xlink:to="loc_us-gaap_PositionDomain_666eff44-9f98-444e-b32c-646967a6311b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongMember_ea1d6686-77bd-4f36-910e-6f205067e786" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PositionDomain_666eff44-9f98-444e-b32c-646967a6311b" xlink:to="loc_us-gaap_LongMember_ea1d6686-77bd-4f36-910e-6f205067e786" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortMember_aaefab22-e69b-4618-b5df-66a2711e10c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShortMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PositionDomain_666eff44-9f98-444e-b32c-646967a6311b" xlink:to="loc_us-gaap_ShortMember_aaefab22-e69b-4618-b5df-66a2711e10c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_36cdd301-502a-4f1b-b7d9-be73c2e5b7ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_47fc99d0-349f-4e7a-95e5-58772c86d657" xlink:to="loc_us-gaap_HedgingDesignationAxis_36cdd301-502a-4f1b-b7d9-be73c2e5b7ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_36cdd301-502a-4f1b-b7d9-be73c2e5b7ab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_36cdd301-502a-4f1b-b7d9-be73c2e5b7ab" xlink:to="loc_us-gaap_HedgingDesignationDomain_36cdd301-502a-4f1b-b7d9-be73c2e5b7ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_fd0dd56d-5e20-48c7-ad78-c2d801711329" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_36cdd301-502a-4f1b-b7d9-be73c2e5b7ab" xlink:to="loc_us-gaap_HedgingDesignationDomain_fd0dd56d-5e20-48c7-ad78-c2d801711329" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_4a94a0d6-b7d2-4344-ac65-77ff20e74ba4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_fd0dd56d-5e20-48c7-ad78-c2d801711329" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_4a94a0d6-b7d2-4344-ac65-77ff20e74ba4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_b27c292c-8b68-4ae7-aee7-c53a12f9ef2c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_47fc99d0-349f-4e7a-95e5-58772c86d657" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_b27c292c-8b68-4ae7-aee7-c53a12f9ef2c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_b27c292c-8b68-4ae7-aee7-c53a12f9ef2c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_b27c292c-8b68-4ae7-aee7-c53a12f9ef2c" xlink:to="loc_us-gaap_HedgingRelationshipDomain_b27c292c-8b68-4ae7-aee7-c53a12f9ef2c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_5ea8f5d1-d295-4e1c-bf8a-6fdbca2652df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_b27c292c-8b68-4ae7-aee7-c53a12f9ef2c" xlink:to="loc_us-gaap_HedgingRelationshipDomain_5ea8f5d1-d295-4e1c-bf8a-6fdbca2652df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentHedgingMember_51f3cfcf-6854-4e56-8814-89111dc79273" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetInvestmentHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_5ea8f5d1-d295-4e1c-bf8a-6fdbca2652df" xlink:to="loc_us-gaap_NetInvestmentHedgingMember_51f3cfcf-6854-4e56-8814-89111dc79273" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/DerivativeFinancialInstrumentsEffectsofDerivativeInstrumentsonOCIandEarningsDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#DerivativeFinancialInstrumentsEffectsofDerivativeInstrumentsonOCIandEarningsDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/DerivativeFinancialInstrumentsEffectsofDerivativeInstrumentsonOCIandEarningsDetails" xlink:type="extended" id="i6c3a3cdc471e4864bf6d79152c16f44c_DerivativeFinancialInstrumentsEffectsofDerivativeInstrumentsonOCIandEarningsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1_64ae84cb-6d53-4c4f-a2b3-8b53b6f69fb4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1_64ae84cb-6d53-4c4f-a2b3-8b53b6f69fb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1_89dd1ba7-1c2f-4ec4-ba4c-e0352b0a2fdf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1_89dd1ba7-1c2f-4ec4-ba4c-e0352b0a2fdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet_3035523f-d82f-49ee-badf-c800fe0e25c5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_GainLossFromComponentsExcludedFromAssessmentOfFairValueHedgeEffectivenessNet_3035523f-d82f-49ee-badf-c800fe0e25c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings_06448131-784d-4f5b-add9-95a155063f97" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings_06448131-784d-4f5b-add9-95a155063f97" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeExcludedComponentGainLossRecognizedInEarnings_3d2f0921-2d95-4d82-817c-5f51d314898f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeExcludedComponentGainLossRecognizedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_DerivativeExcludedComponentGainLossRecognizedInEarnings_3d2f0921-2d95-4d82-817c-5f51d314898f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossBeforeReclassificationAndTax_fea8d1e9-7f49-4668-a873-3b5a70478983" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossBeforeReclassificationAndTax_fea8d1e9-7f49-4668-a873-3b5a70478983" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossReclassificationBeforeTax_a10d1638-bdbf-4288-891d-5af85a7c3a47" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossReclassificationBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossReclassificationBeforeTax_a10d1638-bdbf-4288-891d-5af85a7c3a47" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_1a3a2ab2-a252-4356-bd16-e99631fcf47f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_1a3a2ab2-a252-4356-bd16-e99631fcf47f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeReclassificationForDiscontinuanceBeforeTax_545109db-fd3a-4544-9433-ce044ff4432f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeReclassificationForDiscontinuanceBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeReclassificationForDiscontinuanceBeforeTax_545109db-fd3a-4544-9433-ce044ff4432f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_8b360411-e66e-47a1-a514-b1b38987a849" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_8b360411-e66e-47a1-a514-b1b38987a849" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_a9bf9efe-ffba-4a43-99ab-34685c7c057a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_a9bf9efe-ffba-4a43-99ab-34685c7c057a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20851575-f4bf-4961-92ba-530cccf164c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_b0864c50-839a-4e44-a6d0-a31a2a665928" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20851575-f4bf-4961-92ba-530cccf164c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_e8c7e52e-539f-466a-81f5-3c62ba9de5d5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20851575-f4bf-4961-92ba-530cccf164c0" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_e8c7e52e-539f-466a-81f5-3c62ba9de5d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_e8c7e52e-539f-466a-81f5-3c62ba9de5d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_e8c7e52e-539f-466a-81f5-3c62ba9de5d5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_e8c7e52e-539f-466a-81f5-3c62ba9de5d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_d5a0d84b-6bc3-4d6e-bd5a-3cde7ff990ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_e8c7e52e-539f-466a-81f5-3c62ba9de5d5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_d5a0d84b-6bc3-4d6e-bd5a-3cde7ff990ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_NetSalesMember_4b61ffc5-4d69-469f-837c-7fd3d556090f" xlink:href="wst-20220331.xsd#wst_NetSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d5a0d84b-6bc3-4d6e-bd5a-3cde7ff990ef" xlink:to="loc_wst_NetSalesMember_4b61ffc5-4d69-469f-837c-7fd3d556090f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_87f310dd-01db-4ac6-b9a4-93723e0483e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d5a0d84b-6bc3-4d6e-bd5a-3cde7ff990ef" xlink:to="loc_us-gaap_CostOfSalesMember_87f310dd-01db-4ac6-b9a4-93723e0483e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseMember_5e58122f-3f23-4b78-bdeb-706b0c02736a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d5a0d84b-6bc3-4d6e-bd5a-3cde7ff990ef" xlink:to="loc_us-gaap_InterestExpenseMember_5e58122f-3f23-4b78-bdeb-706b0c02736a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyGainLossMember_9e6ab2d4-f2d1-4221-899c-c81fffad0adf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignCurrencyGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d5a0d84b-6bc3-4d6e-bd5a-3cde7ff990ef" xlink:to="loc_us-gaap_ForeignCurrencyGainLossMember_9e6ab2d4-f2d1-4221-899c-c81fffad0adf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_cb3f2ad4-c5da-48bf-be64-9dc64e699767" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20851575-f4bf-4961-92ba-530cccf164c0" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_cb3f2ad4-c5da-48bf-be64-9dc64e699767" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_cb3f2ad4-c5da-48bf-be64-9dc64e699767_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_cb3f2ad4-c5da-48bf-be64-9dc64e699767" xlink:to="loc_us-gaap_HedgingRelationshipDomain_cb3f2ad4-c5da-48bf-be64-9dc64e699767_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_1669dd71-0b4a-4cb5-8780-1624cfa1a405" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_cb3f2ad4-c5da-48bf-be64-9dc64e699767" xlink:to="loc_us-gaap_HedgingRelationshipDomain_1669dd71-0b4a-4cb5-8780-1624cfa1a405" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_f789b6c1-3b68-4137-b561-d4e583e2ea2f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_1669dd71-0b4a-4cb5-8780-1624cfa1a405" xlink:to="loc_us-gaap_FairValueHedgingMember_f789b6c1-3b68-4137-b561-d4e583e2ea2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_c2210b95-4238-4070-b18e-f00cec7bae03" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_1669dd71-0b4a-4cb5-8780-1624cfa1a405" xlink:to="loc_us-gaap_CashFlowHedgingMember_c2210b95-4238-4070-b18e-f00cec7bae03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentHedgingMember_663d16f9-c98e-40a9-abd7-4937508829d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetInvestmentHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_1669dd71-0b4a-4cb5-8780-1624cfa1a405" xlink:to="loc_us-gaap_NetInvestmentHedgingMember_663d16f9-c98e-40a9-abd7-4937508829d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_5241be43-41ca-45eb-926e-2d4ccb023c87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20851575-f4bf-4961-92ba-530cccf164c0" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_5241be43-41ca-45eb-926e-2d4ccb023c87" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_5241be43-41ca-45eb-926e-2d4ccb023c87_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5241be43-41ca-45eb-926e-2d4ccb023c87" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_5241be43-41ca-45eb-926e-2d4ccb023c87_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_75959b9b-5f66-49fb-bf58-c3d0f6f516fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5241be43-41ca-45eb-926e-2d4ccb023c87" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_75959b9b-5f66-49fb-bf58-c3d0f6f516fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_8490bcc9-9963-4dcc-9fc9-647ce9e4d03f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_75959b9b-5f66-49fb-bf58-c3d0f6f516fe" xlink:to="loc_us-gaap_ForeignExchangeContractMember_8490bcc9-9963-4dcc-9fc9-647ce9e4d03f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryLockMember_1e8001c5-1ad0-46ca-9a4b-d1430175a843" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_75959b9b-5f66-49fb-bf58-c3d0f6f516fe" xlink:to="loc_us-gaap_TreasuryLockMember_1e8001c5-1ad0-46ca-9a4b-d1430175a843" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrencySwapMember_926d3c1c-19ad-46bd-b2b2-d56a50f3b55f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CurrencySwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_75959b9b-5f66-49fb-bf58-c3d0f6f516fe" xlink:to="loc_us-gaap_CurrencySwapMember_926d3c1c-19ad-46bd-b2b2-d56a50f3b55f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityOptionMember_51aa40c5-6c7e-4d9b-88f1-bd161072a907" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommodityOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_75959b9b-5f66-49fb-bf58-c3d0f6f516fe" xlink:to="loc_us-gaap_CommodityOptionMember_51aa40c5-6c7e-4d9b-88f1-bd161072a907" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_e7a6e4da-f697-448e-a30d-809a87d8ac80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20851575-f4bf-4961-92ba-530cccf164c0" xlink:to="loc_us-gaap_HedgingDesignationAxis_e7a6e4da-f697-448e-a30d-809a87d8ac80" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_e7a6e4da-f697-448e-a30d-809a87d8ac80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_e7a6e4da-f697-448e-a30d-809a87d8ac80" xlink:to="loc_us-gaap_HedgingDesignationDomain_e7a6e4da-f697-448e-a30d-809a87d8ac80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_3fafc009-96b2-4753-bfdb-c33dcbdc590e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_e7a6e4da-f697-448e-a30d-809a87d8ac80" xlink:to="loc_us-gaap_HedgingDesignationDomain_3fafc009-96b2-4753-bfdb-c33dcbdc590e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_1cfcb6d1-9906-4590-bfe3-5a985c932125" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_3fafc009-96b2-4753-bfdb-c33dcbdc590e" xlink:to="loc_us-gaap_NondesignatedMember_1cfcb6d1-9906-4590-bfe3-5a985c932125" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/FairValueMeasurementsAssetsandLiabilitiesRecordedatFairValueDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#FairValueMeasurementsAssetsandLiabilitiesRecordedatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/FairValueMeasurementsAssetsandLiabilitiesRecordedatFairValueDetails" xlink:type="extended" id="i64f4a47e704443568f1d544ae34bc99e_FairValueMeasurementsAssetsandLiabilitiesRecordedatFairValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_9352900c-e548-4f58-844e-723dddb7e65b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_3044d794-8267-410f-94e9-a00435096438" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_9352900c-e548-4f58-844e-723dddb7e65b" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_3044d794-8267-410f-94e9-a00435096438" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationPlanAssets_08985903-d592-4217-84fe-6190db812b3e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCompensationPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_3044d794-8267-410f-94e9-a00435096438" xlink:to="loc_us-gaap_DeferredCompensationPlanAssets_08985903-d592-4217-84fe-6190db812b3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_cd199be6-a3b9-4616-b8b4-3b31a1a97bc9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignCurrencyContractAssetFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_3044d794-8267-410f-94e9-a00435096438" xlink:to="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_cd199be6-a3b9-4616-b8b4-3b31a1a97bc9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_467d9b48-0f79-4da3-bde1-b7cf6497ef32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_3044d794-8267-410f-94e9-a00435096438" xlink:to="loc_us-gaap_DerivativeAssets_467d9b48-0f79-4da3-bde1-b7cf6497ef32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_0daf1697-79c1-40bb-9b7e-e52d8a61da49" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_3044d794-8267-410f-94e9-a00435096438" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_0daf1697-79c1-40bb-9b7e-e52d8a61da49" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7a5a6ddf-a344-41ae-aba0-0815e32d2328" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_9352900c-e548-4f58-844e-723dddb7e65b" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7a5a6ddf-a344-41ae-aba0-0815e32d2328" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_c16d1c8a-ac0d-4845-a050-4af7c107b2e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7a5a6ddf-a344-41ae-aba0-0815e32d2328" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_c16d1c8a-ac0d-4845-a050-4af7c107b2e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDeferredCompensationArrangementsLiabilityClassifiedNoncurrent_8857c3d3-9946-42bc-8d10-5ac6717ea42a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherDeferredCompensationArrangementsLiabilityClassifiedNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7a5a6ddf-a344-41ae-aba0-0815e32d2328" xlink:to="loc_us-gaap_OtherDeferredCompensationArrangementsLiabilityClassifiedNoncurrent_8857c3d3-9946-42bc-8d10-5ac6717ea42a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_53497576-9435-47c2-a071-82a583e4637b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7a5a6ddf-a344-41ae-aba0-0815e32d2328" xlink:to="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_53497576-9435-47c2-a071-82a583e4637b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_faea3b90-8457-45c4-935b-6d260df18a44" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7a5a6ddf-a344-41ae-aba0-0815e32d2328" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_faea3b90-8457-45c4-935b-6d260df18a44" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_68d5af08-d1b6-40a0-9f4a-f6ddcb6e5538" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_9352900c-e548-4f58-844e-723dddb7e65b" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_68d5af08-d1b6-40a0-9f4a-f6ddcb6e5538" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0a427775-d545-4fc5-9b77-4c5d5c1a3395" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_68d5af08-d1b6-40a0-9f4a-f6ddcb6e5538" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0a427775-d545-4fc5-9b77-4c5d5c1a3395" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0a427775-d545-4fc5-9b77-4c5d5c1a3395_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0a427775-d545-4fc5-9b77-4c5d5c1a3395" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0a427775-d545-4fc5-9b77-4c5d5c1a3395_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fefe59a8-003d-41c1-b580-5d103091d5bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0a427775-d545-4fc5-9b77-4c5d5c1a3395" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fefe59a8-003d-41c1-b580-5d103091d5bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_fbae53cf-5065-4f8e-9997-c302d198a0a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fefe59a8-003d-41c1-b580-5d103091d5bb" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_fbae53cf-5065-4f8e-9997-c302d198a0a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_e5c2d150-2bb3-43b0-a911-c56e73c9548a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fefe59a8-003d-41c1-b580-5d103091d5bb" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_e5c2d150-2bb3-43b0-a911-c56e73c9548a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_6121e146-b11a-4342-9c4f-e963d9d4798a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fefe59a8-003d-41c1-b580-5d103091d5bb" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_6121e146-b11a-4342-9c4f-e963d9d4798a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_da988010-85d2-41c4-ba3b-6dc7d166f809" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_68d5af08-d1b6-40a0-9f4a-f6ddcb6e5538" xlink:to="loc_us-gaap_FinancialInstrumentAxis_da988010-85d2-41c4-ba3b-6dc7d166f809" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_da988010-85d2-41c4-ba3b-6dc7d166f809_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_da988010-85d2-41c4-ba3b-6dc7d166f809" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_da988010-85d2-41c4-ba3b-6dc7d166f809_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_aa3f6928-1f09-4904-9f4e-2e8a9133fc9f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_da988010-85d2-41c4-ba3b-6dc7d166f809" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_aa3f6928-1f09-4904-9f4e-2e8a9133fc9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrencySwapMember_351971c0-a072-4b9f-8567-1d2ef978f633" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CurrencySwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_aa3f6928-1f09-4904-9f4e-2e8a9133fc9f" xlink:to="loc_us-gaap_CurrencySwapMember_351971c0-a072-4b9f-8567-1d2ef978f633" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityMember_87db878a-6f94-4550-8664-6a60e1db881e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommodityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_aa3f6928-1f09-4904-9f4e-2e8a9133fc9f" xlink:to="loc_us-gaap_CommodityMember_87db878a-6f94-4550-8664-6a60e1db881e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_88170766-cc80-425f-b151-0cc8dd0b2934" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_aa3f6928-1f09-4904-9f4e-2e8a9133fc9f" xlink:to="loc_us-gaap_ForeignExchangeContractMember_88170766-cc80-425f-b151-0cc8dd0b2934" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/AccumulatedOtherComprehensiveLossComponentsofAccumulatedOtherComprehensiveIncomeDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#AccumulatedOtherComprehensiveLossComponentsofAccumulatedOtherComprehensiveIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/AccumulatedOtherComprehensiveLossComponentsofAccumulatedOtherComprehensiveIncomeDetails" xlink:type="extended" id="id0f7f97948fe427db0720e4cdd225584_AccumulatedOtherComprehensiveLossComponentsofAccumulatedOtherComprehensiveIncomeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_f4b3ff10-7552-45e4-982b-8f547b2055c3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a82607d3-dca2-475d-844e-a20194d8d589" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_f4b3ff10-7552-45e4-982b-8f547b2055c3" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a82607d3-dca2-475d-844e-a20194d8d589" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_e233d011-7e93-40d8-a4db-57314da0392c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a82607d3-dca2-475d-844e-a20194d8d589" xlink:to="loc_us-gaap_StockholdersEquity_e233d011-7e93-40d8-a4db-57314da0392c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent_c2d42de9-2b33-4339-a297-98e8be9f64e3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a82607d3-dca2-475d-844e-a20194d8d589" xlink:to="loc_us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent_c2d42de9-2b33-4339-a297-98e8be9f64e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_ecf0dbb0-cc6a-4ab9-b2f7-3fcc0481fd4c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a82607d3-dca2-475d-844e-a20194d8d589" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_ecf0dbb0-cc6a-4ab9-b2f7-3fcc0481fd4c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_66563006-469a-4e5a-bb7d-4f9ad80a2de6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a82607d3-dca2-475d-844e-a20194d8d589" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_66563006-469a-4e5a-bb7d-4f9ad80a2de6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_1a8b0db6-0292-48b6-a23b-fb976db56e83" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_0d3909a6-b941-4fbb-bbe8-63adac1bc7c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_f4b3ff10-7552-45e4-982b-8f547b2055c3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_0d3909a6-b941-4fbb-bbe8-63adac1bc7c2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_2cf2ff5e-c36a-41cc-be68-5a425adc8608" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_0d3909a6-b941-4fbb-bbe8-63adac1bc7c2" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_2cf2ff5e-c36a-41cc-be68-5a425adc8608" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2cf2ff5e-c36a-41cc-be68-5a425adc8608_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_2cf2ff5e-c36a-41cc-be68-5a425adc8608" xlink:to="loc_us-gaap_EquityComponentDomain_2cf2ff5e-c36a-41cc-be68-5a425adc8608_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_604ff6c0-85c6-480a-bc5d-08dfa20c138f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_2cf2ff5e-c36a-41cc-be68-5a425adc8608" xlink:to="loc_us-gaap_EquityComponentDomain_604ff6c0-85c6-480a-bc5d-08dfa20c138f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_5cd7add3-c252-4b20-8fce-b81ae3e7af9d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_604ff6c0-85c6-480a-bc5d-08dfa20c138f" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_5cd7add3-c252-4b20-8fce-b81ae3e7af9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_a40f9f99-505a-49f9-a02e-918d9aac2820" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_5cd7add3-c252-4b20-8fce-b81ae3e7af9d" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_a40f9f99-505a-49f9-a02e-918d9aac2820" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_7569fd43-da69-446b-9891-e3de0d2419b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_5cd7add3-c252-4b20-8fce-b81ae3e7af9d" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_7569fd43-da69-446b-9891-e3de0d2419b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_feebe50f-ab66-450c-b9a6-d0abba0098df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_5cd7add3-c252-4b20-8fce-b81ae3e7af9d" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_feebe50f-ab66-450c-b9a6-d0abba0098df" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_24f5e909-4395-4f90-9889-ba0f283fe891" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_5cd7add3-c252-4b20-8fce-b81ae3e7af9d" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_24f5e909-4395-4f90-9889-ba0f283fe891" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/AccumulatedOtherComprehensiveLossOtherComprehensiveLossReclassificationsDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#AccumulatedOtherComprehensiveLossOtherComprehensiveLossReclassificationsDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/AccumulatedOtherComprehensiveLossOtherComprehensiveLossReclassificationsDetails" xlink:type="extended" id="i5332c75cf05749d7a2de0aeba141a9fd_AccumulatedOtherComprehensiveLossOtherComprehensiveLossReclassificationsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_fad433b8-3bbc-4100-bc8f-9c1b0ef57638" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_fad433b8-3bbc-4100-bc8f-9c1b0ef57638" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_974295fb-aeab-4e68-88ad-3aebc73300ae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_974295fb-aeab-4e68-88ad-3aebc73300ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIncome_2cd165b5-df2d-402b-91d2-75a7d10cb3ae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_OtherIncome_2cd165b5-df2d-402b-91d2-75a7d10cb3ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_3ba3a86b-5e56-4d25-b627-0a8b2985903b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_InterestExpense_3ba3a86b-5e56-4d25-b627-0a8b2985903b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_f417d93c-9f8a-4e7a-ae33-40b054379a17" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_f417d93c-9f8a-4e7a-ae33-40b054379a17" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_290a2481-68b5-425c-96a5-7eae99309f11" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanActuarialGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_290a2481-68b5-425c-96a5-7eae99309f11" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_baec0930-b0e8-4688-a7e2-3c7c26b85055" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_baec0930-b0e8-4688-a7e2-3c7c26b85055" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_9f584ea7-2b50-4514-a3e0-1a72779dd8b4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_9f584ea7-2b50-4514-a3e0-1a72779dd8b4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_fca6161e-97a9-4256-b472-bdb815618171" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_fca6161e-97a9-4256-b472-bdb815618171" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_af1fce03-a547-45db-a297-2f9780e63d93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_NetIncomeLoss_af1fce03-a547-45db-a297-2f9780e63d93" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_97c22f25-fe51-4683-a292-8061f3153495" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_7e70822a-4500-4c30-8ed0-616d121f3ffc" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_97c22f25-fe51-4683-a292-8061f3153495" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_b34a33cc-5bb0-4a16-aea6-310d2f1f8671" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_97c22f25-fe51-4683-a292-8061f3153495" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_b34a33cc-5bb0-4a16-aea6-310d2f1f8671" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_b34a33cc-5bb0-4a16-aea6-310d2f1f8671_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_b34a33cc-5bb0-4a16-aea6-310d2f1f8671" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_b34a33cc-5bb0-4a16-aea6-310d2f1f8671_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_9a9588f5-d9ca-406b-910d-9f33c2affc8e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_b34a33cc-5bb0-4a16-aea6-310d2f1f8671" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_9a9588f5-d9ca-406b-910d-9f33c2affc8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_acfd563f-a441-4643-ae9e-3046f1a86db8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_9a9588f5-d9ca-406b-910d-9f33c2affc8e" xlink:to="loc_us-gaap_ForeignExchangeContractMember_acfd563f-a441-4643-ae9e-3046f1a86db8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryLockMember_07b02b97-e7fb-4ef0-95cd-e1a1a7abedac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryLockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_9a9588f5-d9ca-406b-910d-9f33c2affc8e" xlink:to="loc_us-gaap_TreasuryLockMember_07b02b97-e7fb-4ef0-95cd-e1a1a7abedac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_1ea5a77c-c393-4b73-ad82-b2026c2a33b8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_97c22f25-fe51-4683-a292-8061f3153495" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_1ea5a77c-c393-4b73-ad82-b2026c2a33b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_1ea5a77c-c393-4b73-ad82-b2026c2a33b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_1ea5a77c-c393-4b73-ad82-b2026c2a33b8" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_1ea5a77c-c393-4b73-ad82-b2026c2a33b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_b9158608-6f35-45a6-a958-0e989c774d39" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_1ea5a77c-c393-4b73-ad82-b2026c2a33b8" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_b9158608-6f35-45a6-a958-0e989c774d39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_1fbf6e84-7ac8-48ea-993c-617db9c3f445" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_b9158608-6f35-45a6-a958-0e989c774d39" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_1fbf6e84-7ac8-48ea-993c-617db9c3f445" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_7d3f43ba-b475-4760-a3bd-92f38f2a738d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_97c22f25-fe51-4683-a292-8061f3153495" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_7d3f43ba-b475-4760-a3bd-92f38f2a738d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_7d3f43ba-b475-4760-a3bd-92f38f2a738d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7d3f43ba-b475-4760-a3bd-92f38f2a738d" xlink:to="loc_us-gaap_EquityComponentDomain_7d3f43ba-b475-4760-a3bd-92f38f2a738d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2d29f753-0831-48bd-be68-c95475ecff65" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7d3f43ba-b475-4760-a3bd-92f38f2a738d" xlink:to="loc_us-gaap_EquityComponentDomain_2d29f753-0831-48bd-be68-c95475ecff65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_f2bcba02-684c-4ff0-ac88-3f0f39d823e7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2d29f753-0831-48bd-be68-c95475ecff65" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_f2bcba02-684c-4ff0-ac88-3f0f39d823e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_b48803f9-44d1-4dea-b78f-38269d9300ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2d29f753-0831-48bd-be68-c95475ecff65" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_b48803f9-44d1-4dea-b78f-38269d9300ef" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/ShareholdersEquityChangeinShareholdersEquityDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#ShareholdersEquityChangeinShareholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/ShareholdersEquityChangeinShareholdersEquityDetails" xlink:type="extended" id="i742c832863fa4e068ec79a4907d6aa6d_ShareholdersEquityChangeinShareholdersEquityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_37f29300-1059-4a0b-91a6-06c91be9530c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_37f29300-1059-4a0b-91a6-06c91be9530c" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_a3dee615-64d5-435f-845c-b75188d69aab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_SharesIssued_a3dee615-64d5-435f-845c-b75188d69aab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_1145a2c7-3094-4405-9997-94ca25405087" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_StockholdersEquity_1145a2c7-3094-4405-9997-94ca25405087" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_7596f257-c66c-450d-a494-fe536a7a5de8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_NetIncomeLoss_7596f257-c66c-450d-a494-fe536a7a5de8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_fd94e085-1374-4552-a355-63bf74385db2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_fd94e085-1374-4552-a355-63bf74385db2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_72681c09-dab6-47f3-a789-e91a2d240781" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_72681c09-dab6-47f3-a789-e91a2d240781" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_c7e36691-fdca-4008-8b2d-64846318dd43" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_c7e36691-fdca-4008-8b2d-64846318dd43" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_c4ec8211-f75a-4fe5-8e8b-aebd8bc215ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_c4ec8211-f75a-4fe5-8e8b-aebd8bc215ef" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_0c34b740-220a-474e-8b18-ad6f7bb60a8c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_DividendsCommonStockCash_0c34b740-220a-474e-8b18-ad6f7bb60a8c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_93669114-3b0a-48e1-828e-d93c918cfdcd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7a834e9a-3172-4707-96a5-a2841c974ae7" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_93669114-3b0a-48e1-828e-d93c918cfdcd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_869e51fc-502b-422b-98cc-fedbbb48c5bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_4d32ddfa-d4d1-488b-9f78-25697ef14a96" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_0a98afd5-5644-4dc4-acde-2470d1aeacaa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_37f29300-1059-4a0b-91a6-06c91be9530c" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_0a98afd5-5644-4dc4-acde-2470d1aeacaa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_751a7381-1cf9-4ff9-9767-0ffc8093bcaa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_0a98afd5-5644-4dc4-acde-2470d1aeacaa" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_751a7381-1cf9-4ff9-9767-0ffc8093bcaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_751a7381-1cf9-4ff9-9767-0ffc8093bcaa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_751a7381-1cf9-4ff9-9767-0ffc8093bcaa" xlink:to="loc_us-gaap_EquityComponentDomain_751a7381-1cf9-4ff9-9767-0ffc8093bcaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_50a95587-0ed3-4c8d-baaf-55ebea415bff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_751a7381-1cf9-4ff9-9767-0ffc8093bcaa" xlink:to="loc_us-gaap_EquityComponentDomain_50a95587-0ed3-4c8d-baaf-55ebea415bff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_2e2e916e-3f92-4a88-9716-6e531d16e12c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50a95587-0ed3-4c8d-baaf-55ebea415bff" xlink:to="loc_us-gaap_CommonStockMember_2e2e916e-3f92-4a88-9716-6e531d16e12c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_a50c8083-1d59-4906-828e-e5b85d138217" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50a95587-0ed3-4c8d-baaf-55ebea415bff" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_a50c8083-1d59-4906-828e-e5b85d138217" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember_b71dc3ea-5c8e-4181-a290-6ac2a188fa23" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50a95587-0ed3-4c8d-baaf-55ebea415bff" xlink:to="loc_us-gaap_TreasuryStockMember_b71dc3ea-5c8e-4181-a290-6ac2a188fa23" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_250442f7-f10d-4ece-9e55-8fa98bdadc65" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50a95587-0ed3-4c8d-baaf-55ebea415bff" xlink:to="loc_us-gaap_RetainedEarningsMember_250442f7-f10d-4ece-9e55-8fa98bdadc65" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d001034b-4850-4f93-a6c4-ea5ed07467c7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50a95587-0ed3-4c8d-baaf-55ebea415bff" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d001034b-4850-4f93-a6c4-ea5ed07467c7" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/StockBasedCompensationDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#StockBasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/StockBasedCompensationDetails" xlink:type="extended" id="ia15bb55a2b1043898f2217762326e89d_StockBasedCompensationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_347890e5-96d6-4050-a56a-6fa0b70d8bbc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_347890e5-96d6-4050-a56a-6fa0b70d8bbc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_7a56e49e-d7da-44b5-b151-8d23b7ee8fbd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_7a56e49e-d7da-44b5-b151-8d23b7ee8fbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_86e2349a-711d-4d25-8b22-342af82d1f60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_86e2349a-711d-4d25-8b22-342af82d1f60" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_cd4efe88-c20a-4b4f-9494-b25eb297ce12" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_cd4efe88-c20a-4b4f-9494-b25eb297ce12" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_00cffc51-05d7-48d8-a10b-52148c7a8ca5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_00cffc51-05d7-48d8-a10b-52148c7a8ca5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_d5957a4d-911d-40bd-906d-d5413e1755f6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_d5957a4d-911d-40bd-906d-d5413e1755f6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_e94f123f-9f99-4988-bbfa-e56c4474ed3b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_e94f123f-9f99-4988-bbfa-e56c4474ed3b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_5b5c71a2-6373-41df-a2c9-4b299276924d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_5b5c71a2-6373-41df-a2c9-4b299276924d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_90c7d8be-8ff5-4e04-9e02-63a7e9e8810e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_90c7d8be-8ff5-4e04-9e02-63a7e9e8810e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d2b3aea1-033d-44ec-a706-76912548016a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d2b3aea1-033d-44ec-a706-76912548016a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_ShareBasedCompensationArrangementByShareBasedPaymentAwardActualPayoutPercentage_7d254ee8-7ef0-489c-a4e5-9607cebff5f5" xlink:href="wst-20220331.xsd#wst_ShareBasedCompensationArrangementByShareBasedPaymentAwardActualPayoutPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_wst_ShareBasedCompensationArrangementByShareBasedPaymentAwardActualPayoutPercentage_7d254ee8-7ef0-489c-a4e5-9607cebff5f5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_eb0fd954-35f1-4f16-8512-a1110a2d5858" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_eb0fd954-35f1-4f16-8512-a1110a2d5858" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dbe04eea-6178-4afb-91fd-58dde1c26304" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9ab569da-26bc-492a-aae5-3e43becc9725" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dbe04eea-6178-4afb-91fd-58dde1c26304" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_2fd84b1e-f332-4ece-8709-d84776258d97" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dbe04eea-6178-4afb-91fd-58dde1c26304" xlink:to="loc_us-gaap_AwardTypeAxis_2fd84b1e-f332-4ece-8709-d84776258d97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2fd84b1e-f332-4ece-8709-d84776258d97_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_2fd84b1e-f332-4ece-8709-d84776258d97" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2fd84b1e-f332-4ece-8709-d84776258d97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5d5048f8-e9bf-4570-909c-180544b9a1b1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_2fd84b1e-f332-4ece-8709-d84776258d97" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5d5048f8-e9bf-4570-909c-180544b9a1b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_8e459879-c7c9-44fc-9a3c-8d2d63457558" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5d5048f8-e9bf-4570-909c-180544b9a1b1" xlink:to="loc_us-gaap_PerformanceSharesMember_8e459879-c7c9-44fc-9a3c-8d2d63457558" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_f770608d-f680-4db6-b4bf-d9e71bcd78c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5d5048f8-e9bf-4570-909c-180544b9a1b1" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_f770608d-f680-4db6-b4bf-d9e71bcd78c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_0cfaacf3-2ed3-410b-95b7-12e8cacfa176" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dbe04eea-6178-4afb-91fd-58dde1c26304" xlink:to="loc_srt_RangeAxis_0cfaacf3-2ed3-410b-95b7-12e8cacfa176" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0cfaacf3-2ed3-410b-95b7-12e8cacfa176_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_0cfaacf3-2ed3-410b-95b7-12e8cacfa176" xlink:to="loc_srt_RangeMember_0cfaacf3-2ed3-410b-95b7-12e8cacfa176_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1d811cc4-a2b2-44c8-ad4d-92ce9912cb9b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_0cfaacf3-2ed3-410b-95b7-12e8cacfa176" xlink:to="loc_srt_RangeMember_1d811cc4-a2b2-44c8-ad4d-92ce9912cb9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_f4d40b18-a329-4e32-bdf0-29400c424298" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1d811cc4-a2b2-44c8-ad4d-92ce9912cb9b" xlink:to="loc_srt_MinimumMember_f4d40b18-a329-4e32-bdf0-29400c424298" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_66520f6e-8519-4008-b824-71f15eef39c5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1d811cc4-a2b2-44c8-ad4d-92ce9912cb9b" xlink:to="loc_srt_MaximumMember_66520f6e-8519-4008-b824-71f15eef39c5" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/BenefitPlansScheduleofComponentsofNetPeriodicBenefitCostDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#BenefitPlansScheduleofComponentsofNetPeriodicBenefitCostDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/BenefitPlansScheduleofComponentsofNetPeriodicBenefitCostDetails" xlink:type="extended" id="i6aa80d99815143f696f089d18d7ab860_BenefitPlansScheduleofComponentsofNetPeriodicBenefitCostDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_d1781461-76d4-41af-bab7-857a439103f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_d1781461-76d4-41af-bab7-857a439103f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_0dafd981-e343-4beb-b401-9f35bfe14a1a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_0dafd981-e343-4beb-b401-9f35bfe14a1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_7ce92d2f-29c7-4b68-8d4f-771698eae45c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_7ce92d2f-29c7-4b68-8d4f-771698eae45c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_93d71034-68a7-490f-9d6c-50407ba03d77" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_93d71034-68a7-490f-9d6c-50407ba03d77" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_3a16d7a8-700b-4bde-93da-9e90bf914446" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanActuarialGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlanActuarialGainLoss_3a16d7a8-700b-4bde-93da-9e90bf914446" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_4e6a05c0-0071-4567-b394-6f682372c05c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_4e6a05c0-0071-4567-b394-6f682372c05c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_b6dbaacc-21c4-469d-8cca-5e083d98d536" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_b6dbaacc-21c4-469d-8cca-5e083d98d536" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_00362d78-c654-4602-ade2-b02c77851471" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_194505d1-ab61-47bd-be83-c72f479e82da" xlink:to="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_00362d78-c654-4602-ade2-b02c77851471" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_2e6e68c5-3dee-46fe-82a4-e21ddbff07ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_00362d78-c654-4602-ade2-b02c77851471" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_2e6e68c5-3dee-46fe-82a4-e21ddbff07ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_2e6e68c5-3dee-46fe-82a4-e21ddbff07ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_2e6e68c5-3dee-46fe-82a4-e21ddbff07ad" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_2e6e68c5-3dee-46fe-82a4-e21ddbff07ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_79d48efc-07ce-45cf-b2fd-d44886772e5c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_2e6e68c5-3dee-46fe-82a4-e21ddbff07ad" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_79d48efc-07ce-45cf-b2fd-d44886772e5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_41cf43f0-708b-40bd-b20e-ccf2f578f911" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_79d48efc-07ce-45cf-b2fd-d44886772e5c" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_41cf43f0-708b-40bd-b20e-ccf2f578f911" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_fedf6e86-1b95-4371-825b-a3631a3f6897" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_79d48efc-07ce-45cf-b2fd-d44886772e5c" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_fedf6e86-1b95-4371-825b-a3631a3f6897" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationAxis_ff11e707-773e-4beb-bd54-76a0eabcbf73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanSponsorLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_00362d78-c654-4602-ade2-b02c77851471" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationAxis_ff11e707-773e-4beb-bd54-76a0eabcbf73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_ff11e707-773e-4beb-bd54-76a0eabcbf73_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_ff11e707-773e-4beb-bd54-76a0eabcbf73" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_ff11e707-773e-4beb-bd54-76a0eabcbf73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_fe36fb58-5d7f-4f0c-abb2-173278952bbb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_ff11e707-773e-4beb-bd54-76a0eabcbf73" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_fe36fb58-5d7f-4f0c-abb2-173278952bbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticPlanMember_f012c2b9-da1c-4cb0-927f-230384e4650b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DomesticPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationDomain_fe36fb58-5d7f-4f0c-abb2-173278952bbb" xlink:to="loc_us-gaap_DomesticPlanMember_f012c2b9-da1c-4cb0-927f-230384e4650b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_b669d54f-06a0-40be-8218-ce0b0e06109f" xlink:href="https://xbrl.sec.gov/country/2021/country-2021.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticPlanMember_f012c2b9-da1c-4cb0-927f-230384e4650b" xlink:to="loc_country_US_b669d54f-06a0-40be-8218-ce0b0e06109f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignPlanMember_004989dc-b31d-4c1f-b27a-829676041289" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationDomain_fe36fb58-5d7f-4f0c-abb2-173278952bbb" xlink:to="loc_us-gaap_ForeignPlanMember_004989dc-b31d-4c1f-b27a-829676041289" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/BenefitPlansNarrativeDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#BenefitPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/BenefitPlansNarrativeDetails" xlink:type="extended" id="i27b29578ec5b4ccb94cd5fa1b22e911b_BenefitPlansNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_f981e457-27bd-4885-98e5-a5e8c4dbd8b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_f374ce0f-5f01-4369-8086-594d3b647276" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_f981e457-27bd-4885-98e5-a5e8c4dbd8b2" xlink:to="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_f374ce0f-5f01-4369-8086-594d3b647276" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_7bccf3de-cca3-495d-bafc-c63044a7ca96" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_f981e457-27bd-4885-98e5-a5e8c4dbd8b2" xlink:to="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_7bccf3de-cca3-495d-bafc-c63044a7ca96" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_63bf9100-431e-453a-bc28-c3418277dc83" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_7bccf3de-cca3-495d-bafc-c63044a7ca96" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_63bf9100-431e-453a-bc28-c3418277dc83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_63bf9100-431e-453a-bc28-c3418277dc83_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_63bf9100-431e-453a-bc28-c3418277dc83" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_63bf9100-431e-453a-bc28-c3418277dc83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_298b2cc0-ebac-48e4-b66b-7df1efeeedf2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_63bf9100-431e-453a-bc28-c3418277dc83" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_298b2cc0-ebac-48e4-b66b-7df1efeeedf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_cd12297a-0fd8-45bd-a532-08230b46eb28" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_298b2cc0-ebac-48e4-b66b-7df1efeeedf2" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_cd12297a-0fd8-45bd-a532-08230b46eb28" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/OtherIncomeExpenseNarrativeDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#OtherIncomeExpenseNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/OtherIncomeExpenseNarrativeDetails" xlink:type="extended" id="i8cd0322ed0a44521b67cfdc6d3c2bbc5_OtherIncomeExpenseNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_6e19acd2-b8af-4e5a-8c11-8c72259ac5c5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SummaryOfInvestmentHoldingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_RestructuringAndRelatedActivitiesPeriodOfImplementation_ac16f0a6-bb8b-48b8-b4ed-d988087f60b7" xlink:href="wst-20220331.xsd#wst_RestructuringAndRelatedActivitiesPeriodOfImplementation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_6e19acd2-b8af-4e5a-8c11-8c72259ac5c5" xlink:to="loc_wst_RestructuringAndRelatedActivitiesPeriodOfImplementation_ac16f0a6-bb8b-48b8-b4ed-d988087f60b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_59c45e31-c653-49ae-a511-4305555f1f19" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_6e19acd2-b8af-4e5a-8c11-8c72259ac5c5" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_59c45e31-c653-49ae-a511-4305555f1f19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOnFutureEarningsAmount_2bc35a53-a971-4c78-9569-4885efe1ab04" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectOnFutureEarningsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_6e19acd2-b8af-4e5a-8c11-8c72259ac5c5" xlink:to="loc_us-gaap_EffectOnFutureEarningsAmount_2bc35a53-a971-4c78-9569-4885efe1ab04" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_3fac1140-11e7-4787-95d3-da6b78125ac2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringAndRelatedCostCostIncurredToDate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_6e19acd2-b8af-4e5a-8c11-8c72259ac5c5" xlink:to="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_3fac1140-11e7-4787-95d3-da6b78125ac2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfInvestmentHoldingsTable_4e7222ab-0bc5-4dab-80be-8ef00275c8bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SummaryOfInvestmentHoldingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_6e19acd2-b8af-4e5a-8c11-8c72259ac5c5" xlink:to="loc_us-gaap_SummaryOfInvestmentHoldingsTable_4e7222ab-0bc5-4dab-80be-8ef00275c8bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e6a9c7f2-d067-4a91-addd-7121b5637f1c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsTable_4e7222ab-0bc5-4dab-80be-8ef00275c8bf" xlink:to="loc_srt_RangeAxis_e6a9c7f2-d067-4a91-addd-7121b5637f1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e6a9c7f2-d067-4a91-addd-7121b5637f1c_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e6a9c7f2-d067-4a91-addd-7121b5637f1c" xlink:to="loc_srt_RangeMember_e6a9c7f2-d067-4a91-addd-7121b5637f1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ab8397ba-d728-4d40-bc73-38e4d9a701cd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e6a9c7f2-d067-4a91-addd-7121b5637f1c" xlink:to="loc_srt_RangeMember_ab8397ba-d728-4d40-bc73-38e4d9a701cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_6b328ea5-3a01-4faa-a111-c6f708121894" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_ab8397ba-d728-4d40-bc73-38e4d9a701cd" xlink:to="loc_srt_MinimumMember_6b328ea5-3a01-4faa-a111-c6f708121894" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_05e7a18c-7144-42ea-ba23-158fc5b9d9e1" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_ab8397ba-d728-4d40-bc73-38e4d9a701cd" xlink:to="loc_srt_MaximumMember_05e7a18c-7144-42ea-ba23-158fc5b9d9e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_e9cef67d-bcf0-4119-927a-badf21944012" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsTable_4e7222ab-0bc5-4dab-80be-8ef00275c8bf" xlink:to="loc_us-gaap_RestructuringPlanAxis_e9cef67d-bcf0-4119-927a-badf21944012" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_e9cef67d-bcf0-4119-927a-badf21944012_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_e9cef67d-bcf0-4119-927a-badf21944012" xlink:to="loc_us-gaap_RestructuringPlanDomain_e9cef67d-bcf0-4119-927a-badf21944012_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_7a4cc98c-8305-4051-8e14-c5eb34b8fac3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_e9cef67d-bcf0-4119-927a-badf21944012" xlink:to="loc_us-gaap_RestructuringPlanDomain_7a4cc98c-8305-4051-8e14-c5eb34b8fac3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_The2020RestructuringPlanMember_38eb94ed-e1f6-4822-9ded-48333490251d" xlink:href="wst-20220331.xsd#wst_The2020RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_7a4cc98c-8305-4051-8e14-c5eb34b8fac3" xlink:to="loc_wst_The2020RestructuringPlanMember_38eb94ed-e1f6-4822-9ded-48333490251d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/OtherIncomeExpenseScheduleofRestructuringandRelatedChargesDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#OtherIncomeExpenseScheduleofRestructuringandRelatedChargesDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/OtherIncomeExpenseScheduleofRestructuringandRelatedChargesDetails" xlink:type="extended" id="if8ca0994f47f408a91e5ddc1cae96d42_OtherIncomeExpenseScheduleofRestructuringandRelatedChargesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_49f0d780-b34f-4e64-9e13-06f1c27c1222" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_78a87d91-7bec-4863-b89a-6d680e6ab24c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_49f0d780-b34f-4e64-9e13-06f1c27c1222" xlink:to="loc_us-gaap_RestructuringReserveRollForward_78a87d91-7bec-4863-b89a-6d680e6ab24c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_3df28cf7-0305-4889-8a31-652bb9809769" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_78a87d91-7bec-4863-b89a-6d680e6ab24c" xlink:to="loc_us-gaap_RestructuringReserve_3df28cf7-0305-4889-8a31-652bb9809769" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_b91089c3-4b53-4a23-9d33-6860424b5028" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_78a87d91-7bec-4863-b89a-6d680e6ab24c" xlink:to="loc_us-gaap_RestructuringCharges_b91089c3-4b53-4a23-9d33-6860424b5028" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_fe71c893-552a-4fb0-8430-0919d8201a98" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_78a87d91-7bec-4863-b89a-6d680e6ab24c" xlink:to="loc_us-gaap_PaymentsForRestructuring_fe71c893-552a-4fb0-8430-0919d8201a98" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_2fa4cc14-2445-4fa1-838b-2fca01ec1813" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringReserve"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_440c894e-267f-46ee-8534-30d212b6cdf1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_49f0d780-b34f-4e64-9e13-06f1c27c1222" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_440c894e-267f-46ee-8534-30d212b6cdf1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_6f555ef9-ee91-47da-8b99-9c25b2b290c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_440c894e-267f-46ee-8534-30d212b6cdf1" xlink:to="loc_us-gaap_RestructuringPlanAxis_6f555ef9-ee91-47da-8b99-9c25b2b290c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_6f555ef9-ee91-47da-8b99-9c25b2b290c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_6f555ef9-ee91-47da-8b99-9c25b2b290c0" xlink:to="loc_us-gaap_RestructuringPlanDomain_6f555ef9-ee91-47da-8b99-9c25b2b290c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_21d99502-f2bd-4518-af66-9f0df8cf582c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_6f555ef9-ee91-47da-8b99-9c25b2b290c0" xlink:to="loc_us-gaap_RestructuringPlanDomain_21d99502-f2bd-4518-af66-9f0df8cf582c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_A2020RestructuringPlanMember_21f95c7e-f5e5-40bc-b40f-d154dbd427f9" xlink:href="wst-20220331.xsd#wst_A2020RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_21d99502-f2bd-4518-af66-9f0df8cf582c" xlink:to="loc_wst_A2020RestructuringPlanMember_21f95c7e-f5e5-40bc-b40f-d154dbd427f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_8bd4286c-c511-4354-8dd9-6e8b7fccb1cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_440c894e-267f-46ee-8534-30d212b6cdf1" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_8bd4286c-c511-4354-8dd9-6e8b7fccb1cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_8bd4286c-c511-4354-8dd9-6e8b7fccb1cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_8bd4286c-c511-4354-8dd9-6e8b7fccb1cc" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_8bd4286c-c511-4354-8dd9-6e8b7fccb1cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_8b3458f0-da73-4369-a087-ee2792983ed8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_8bd4286c-c511-4354-8dd9-6e8b7fccb1cc" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_8b3458f0-da73-4369-a087-ee2792983ed8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_9fa01792-5768-4fb2-ba9b-e289635c2563" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_8b3458f0-da73-4369-a087-ee2792983ed8" xlink:to="loc_us-gaap_EmployeeSeveranceMember_9fa01792-5768-4fb2-ba9b-e289635c2563" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_2ef344aa-38ef-4408-94b9-f316122ff420" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_8b3458f0-da73-4369-a087-ee2792983ed8" xlink:to="loc_us-gaap_OtherRestructuringMember_2ef344aa-38ef-4408-94b9-f316122ff420" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/OtherIncomeExpenseOtherItemsDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#OtherIncomeExpenseOtherItemsDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/OtherIncomeExpenseOtherItemsDetails" xlink:type="extended" id="i1064809cf3564dae867cbbd6a66701b4_OtherIncomeExpenseOtherItemsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ee5c9496-5342-46af-a54e-eb3776979eff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_48fc09bc-7fc0-452e-b02c-5c8c629ebd7a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ee5c9496-5342-46af-a54e-eb3776979eff" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_48fc09bc-7fc0-452e-b02c-5c8c629ebd7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfInvestments_de02c1c2-492b-4f75-8699-37f02e57831e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ImpairmentOfInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ee5c9496-5342-46af-a54e-eb3776979eff" xlink:to="loc_us-gaap_ImpairmentOfInvestments_de02c1c2-492b-4f75-8699-37f02e57831e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ef5f15eb-22b8-4714-bd81-a76e2e65b0e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ee5c9496-5342-46af-a54e-eb3776979eff" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ef5f15eb-22b8-4714-bd81-a76e2e65b0e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_787a31fa-b431-4ef7-9818-d9fab266c059" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ef5f15eb-22b8-4714-bd81-a76e2e65b0e6" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_787a31fa-b431-4ef7-9818-d9fab266c059" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_787a31fa-b431-4ef7-9818-d9fab266c059_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_787a31fa-b431-4ef7-9818-d9fab266c059" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_787a31fa-b431-4ef7-9818-d9fab266c059_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_c2da775b-54eb-4b23-b187-f227051e4558" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_787a31fa-b431-4ef7-9818-d9fab266c059" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_c2da775b-54eb-4b23-b187-f227051e4558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityOptionMember_13db0acd-0921-4984-95fc-bb030eeb8140" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommodityOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_c2da775b-54eb-4b23-b187-f227051e4558" xlink:to="loc_us-gaap_CommodityOptionMember_13db0acd-0921-4984-95fc-bb030eeb8140" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_d4aa315a-3911-41cc-9cb1-6b325a7eb7f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ef5f15eb-22b8-4714-bd81-a76e2e65b0e6" xlink:to="loc_us-gaap_HedgingDesignationAxis_d4aa315a-3911-41cc-9cb1-6b325a7eb7f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_d4aa315a-3911-41cc-9cb1-6b325a7eb7f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_d4aa315a-3911-41cc-9cb1-6b325a7eb7f4" xlink:to="loc_us-gaap_HedgingDesignationDomain_d4aa315a-3911-41cc-9cb1-6b325a7eb7f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_9cd7a277-a64a-4dc5-9bcf-4812fba39f51" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_d4aa315a-3911-41cc-9cb1-6b325a7eb7f4" xlink:to="loc_us-gaap_HedgingDesignationDomain_9cd7a277-a64a-4dc5-9bcf-4812fba39f51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_b34d042d-3e64-416a-b770-c64e539dade2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_9cd7a277-a64a-4dc5-9bcf-4812fba39f51" xlink:to="loc_us-gaap_NondesignatedMember_b34d042d-3e64-416a-b770-c64e539dade2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_c058f327-4714-4e2f-9a8c-1e23b161add9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ef5f15eb-22b8-4714-bd81-a76e2e65b0e6" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_c058f327-4714-4e2f-9a8c-1e23b161add9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_c058f327-4714-4e2f-9a8c-1e23b161add9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_c058f327-4714-4e2f-9a8c-1e23b161add9" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_c058f327-4714-4e2f-9a8c-1e23b161add9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_a9deeeda-a90d-4004-b62d-89e1e6c3ab8b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_c058f327-4714-4e2f-9a8c-1e23b161add9" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_a9deeeda-a90d-4004-b62d-89e1e6c3ab8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyGainLossMember_3510ec31-21b2-43c5-9c71-f69a0b3eeae0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ForeignCurrencyGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a9deeeda-a90d-4004-b62d-89e1e6c3ab8b" xlink:to="loc_us-gaap_ForeignCurrencyGainLossMember_3510ec31-21b2-43c5-9c71-f69a0b3eeae0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/SegmentInformationSalesbyProductGroupDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#SegmentInformationSalesbyProductGroupDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/SegmentInformationSalesbyProductGroupDetails" xlink:type="extended" id="i12bb7b3ad339407faf0054fa8f98805b_SegmentInformationSalesbyProductGroupDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_40ce39eb-7ab3-4098-8f8c-eb9aae8bcfca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_9624b13c-c1eb-4829-aed9-bf899d530d75" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_40ce39eb-7ab3-4098-8f8c-eb9aae8bcfca" xlink:to="loc_us-gaap_Revenues_9624b13c-c1eb-4829-aed9-bf899d530d75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_f595ea02-c328-4f4a-a77b-c311d8b066d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_40ce39eb-7ab3-4098-8f8c-eb9aae8bcfca" xlink:to="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_f595ea02-c328-4f4a-a77b-c311d8b066d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_ad325d32-7748-44a2-992e-b923cb01c941" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_f595ea02-c328-4f4a-a77b-c311d8b066d2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_ad325d32-7748-44a2-992e-b923cb01c941" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_ad325d32-7748-44a2-992e-b923cb01c941_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ad325d32-7748-44a2-992e-b923cb01c941" xlink:to="loc_us-gaap_SegmentDomain_ad325d32-7748-44a2-992e-b923cb01c941_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4118d196-7380-4944-933f-e5e8cf0eb0dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ad325d32-7748-44a2-992e-b923cb01c941" xlink:to="loc_us-gaap_SegmentDomain_4118d196-7380-4944-933f-e5e8cf0eb0dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_ProprietaryProductsMember_cc50f028-bb04-4f60-ba49-32a587109500" xlink:href="wst-20220331.xsd#wst_ProprietaryProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4118d196-7380-4944-933f-e5e8cf0eb0dd" xlink:to="loc_wst_ProprietaryProductsMember_cc50f028-bb04-4f60-ba49-32a587109500" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_ContractManufacturedProductsMember_e97eece2-5266-468a-b255-1cb18cef2c7b" xlink:href="wst-20220331.xsd#wst_ContractManufacturedProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4118d196-7380-4944-933f-e5e8cf0eb0dd" xlink:to="loc_wst_ContractManufacturedProductsMember_e97eece2-5266-468a-b255-1cb18cef2c7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_274abc03-09b9-4be5-89b3-4fa16fdf5ff8" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_f595ea02-c328-4f4a-a77b-c311d8b066d2" xlink:to="loc_srt_ConsolidationItemsAxis_274abc03-09b9-4be5-89b3-4fa16fdf5ff8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_274abc03-09b9-4be5-89b3-4fa16fdf5ff8_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_274abc03-09b9-4be5-89b3-4fa16fdf5ff8" xlink:to="loc_srt_ConsolidationItemsDomain_274abc03-09b9-4be5-89b3-4fa16fdf5ff8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_74289a81-3314-4dc7-b511-2ed25f1f47a6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_274abc03-09b9-4be5-89b3-4fa16fdf5ff8" xlink:to="loc_srt_ConsolidationItemsDomain_74289a81-3314-4dc7-b511-2ed25f1f47a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_7fa6d815-12c1-4ffe-8102-3bc624ea9f06" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_74289a81-3314-4dc7-b511-2ed25f1f47a6" xlink:to="loc_us-gaap_OperatingSegmentsMember_7fa6d815-12c1-4ffe-8102-3bc624ea9f06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_60909846-5a20-456b-bb5a-e7213572ae60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_74289a81-3314-4dc7-b511-2ed25f1f47a6" xlink:to="loc_us-gaap_IntersegmentEliminationMember_60909846-5a20-456b-bb5a-e7213572ae60" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westpharma.com/role/SegmentInformationSegmentFinancialInformationDetails" xlink:type="simple" xlink:href="wst-20220331.xsd#SegmentInformationSegmentFinancialInformationDetails"/>
  <link:definitionLink xlink:role="http://www.westpharma.com/role/SegmentInformationSegmentFinancialInformationDetails" xlink:type="extended" id="ibfcd01bd37b54089a16ae168c4b9ec73_SegmentInformationSegmentFinancialInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_e79c7928-3dcd-449c-a63a-4bfda5bb98cb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_OperatingIncomeLoss_e79c7928-3dcd-449c-a63a-4bfda5bb98cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_86eacebf-2036-45b2-8293-d2c8b73d7abb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_ShareBasedCompensation_86eacebf-2036-45b2-8293-d2c8b73d7abb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_2a282d2a-5aad-4c71-a781-022576572f16" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_2a282d2a-5aad-4c71-a781-022576572f16" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_aca153ee-5a65-4334-8e19-d9f10d983033" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_RestructuringCharges_aca153ee-5a65-4334-8e19-d9f10d983033" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_02a1d4b7-86d9-4cc8-a320-722a96aa1014" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_02a1d4b7-86d9-4cc8-a320-722a96aa1014" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_CostInvestmentImpairment_b1325db1-480e-473d-9317-b3f932c91feb" xlink:href="wst-20220331.xsd#wst_CostInvestmentImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_wst_CostInvestmentImpairment_b1325db1-480e-473d-9317-b3f932c91feb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_c2e569a9-8bf9-420a-b778-986b6f258274" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_c2e569a9-8bf9-420a-b778-986b6f258274" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_412432bf-941d-4425-9ef8-a0ae83fa58ba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_412432bf-941d-4425-9ef8-a0ae83fa58ba" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_ab944113-c876-4d56-b04f-642817d4ae03" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2232bede-1b5b-4a6a-84a2-6dd7b5de719f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_ab944113-c876-4d56-b04f-642817d4ae03" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_81858f96-5cec-4e01-b798-36d44e0b5d6a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_ab944113-c876-4d56-b04f-642817d4ae03" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_81858f96-5cec-4e01-b798-36d44e0b5d6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_81858f96-5cec-4e01-b798-36d44e0b5d6a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_81858f96-5cec-4e01-b798-36d44e0b5d6a" xlink:to="loc_us-gaap_SegmentDomain_81858f96-5cec-4e01-b798-36d44e0b5d6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_bda41c90-8885-423b-bc80-8cbb100a3078" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_81858f96-5cec-4e01-b798-36d44e0b5d6a" xlink:to="loc_us-gaap_SegmentDomain_bda41c90-8885-423b-bc80-8cbb100a3078" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_ProprietaryProductsMember_cf8065aa-8c8e-4813-9743-5838d665bba7" xlink:href="wst-20220331.xsd#wst_ProprietaryProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_bda41c90-8885-423b-bc80-8cbb100a3078" xlink:to="loc_wst_ProprietaryProductsMember_cf8065aa-8c8e-4813-9743-5838d665bba7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wst_ContractManufacturedProductsMember_d0f3677a-294b-4611-af20-4f5cea1cd47b" xlink:href="wst-20220331.xsd#wst_ContractManufacturedProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_bda41c90-8885-423b-bc80-8cbb100a3078" xlink:to="loc_wst_ContractManufacturedProductsMember_d0f3677a-294b-4611-af20-4f5cea1cd47b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_000dd4d3-a3c1-4c9d-82c3-c68bd185d567" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_ab944113-c876-4d56-b04f-642817d4ae03" xlink:to="loc_srt_ConsolidationItemsAxis_000dd4d3-a3c1-4c9d-82c3-c68bd185d567" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_000dd4d3-a3c1-4c9d-82c3-c68bd185d567_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_000dd4d3-a3c1-4c9d-82c3-c68bd185d567" xlink:to="loc_srt_ConsolidationItemsDomain_000dd4d3-a3c1-4c9d-82c3-c68bd185d567_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_6e1a7cd7-0140-45e4-a839-f64b169bfdee" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_000dd4d3-a3c1-4c9d-82c3-c68bd185d567" xlink:to="loc_srt_ConsolidationItemsDomain_6e1a7cd7-0140-45e4-a839-f64b169bfdee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_a2162b64-d4c8-4571-97c0-3eab597138e0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_6e1a7cd7-0140-45e4-a839-f64b169bfdee" xlink:to="loc_us-gaap_OperatingSegmentsMember_a2162b64-d4c8-4571-97c0-3eab597138e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_964bf245-5229-4a08-8db7-b5299f92d603" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_6e1a7cd7-0140-45e4-a839-f64b169bfdee" xlink:to="loc_us-gaap_CorporateNonSegmentMember_964bf245-5229-4a08-8db7-b5299f92d603" xlink:type="arc" order="1"/>
  </link:definitionLink>
</link:linkbase>
