<p><strong>Noun</strong></p><ul><li>a pin inserted through the end of an axletree to keep the wheel on</li><li>something that holds the various elements of a complicated structure together: The monarchy was the linchpin of the nation's traditions and society</li></ul><p><strong>Synonyms</strong></p><ul><li>prop</li><li>anchor</li><li>bulwark</li><li>pillar</li></ul>