lynchpin
 制輪楔;輪轄
 lynchpin
      n 1: 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]
      2: pin inserted through an axletree to hold a wheel on [syn: linchpin]