linchpin
    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,
         lynchpin]
    2: pin inserted through an axletree to hold a wheel on [syn:
       linchpin, lynchpin]

Linchpin \Linch"pin`\ (l[i^]nch"p[i^]n`), n. [AS. lynis the
   axletree; akin to D. luns linchpin, OS. lunisa, LG. lunse, G.
   l["u]nse, OHG. lun peg, bolt.]
   A pin used to prevent the wheel of a vehicle from sliding off
   the axletree.
   [1913 Webster]