n.
Variant: also lynch · pin
Pronunciation: ' linch- ˌ pin
Function: noun
Etymology: Middle English lynspin, from lyns linchpin (fr. Old English lynis ) + pin; akin to Middle High German luns linchpin
Date: 13th century
1 : a locking pin inserted crosswise (as through the end of an axle or shaft)
2 : one that serves to hold together parts or elements that exist or function as a unit <the linchpin in the defense's case>