'lynchpin' definitions:

Definition of 'lynchpin'

(from WordNet)
noun
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" [syn: anchor, mainstay, keystone, backbone, linchpin, lynchpin]
noun
Pin inserted through an axletree to hold a wheel on [syn: linchpin, lynchpin]