definition of
linchpin

[1] #1 linchpin n. [anchor, mainstay, keystone, backbone, lynchpin] a central cohesive source of support and stability; "faith is his anchor"; "the keystone of campaign reform was the ban on soft money"; "he is the linchpin of this firm". wn

[2] #2 linchpin n. [lynchpin] pin inserted through an axletree to hold a wheel on. wn