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<!-- DFIN New ActiveDisclosure (SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date :2023-03-30T16:36:27.3674+00:00 -->
<!-- Copyright (c) 2023 Donnelly Financial Solutions, Inc. All Rights Reserved. -->
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    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrivatePlacementMember" xlink:label="us-gaap_PrivatePlacementMember"/>
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  <link:definitionLink xlink:type="extended" xlink:role="http://www.eledon.com/20221231/taxonomy/role/Role_DisclosureStockholdersEquityScheduleOfWarrantToPurchaseSeriesX1ConvertiblePreferredStockActivityDetail">
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    <link:loc xlink:type="locator" xlink:href="eldn-20221231.xsd#eldn_WarrantsAssumedAndReplacedInAcquisitionMember" xlink:label="eldn_WarrantsAssumedAndReplacedInAcquisitionMember"/>
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