Source : WordNet®

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}]