Linchpin
Pronunciation : Linch"pin`
Part of Speech : n.
Etymology : [AS. lynis the axletree; akin to D. luns linchpin, OS. lunisa, LG. lunse, G. l?nse, OHG. lun peg, bolt.]
Definition : Defn: A pin used to prevent the wheel of a vehicle from sliding off the axletree.
Source : Webster's Unabridged Dictionary, 1913