Dictionary
linch•pin
Pronunciation: (linch'pin"), [key]—
n.
1. a pin inserted through the end of an axletree to keep the wheel on.
2. something that holds the various elements of a complicated structure together:
The monarchy was the linchpin of the nation's traditions and society. Also,lynchpin.Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.