variants:
or less commonly lynchpin
Definition of linchpin
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
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Merriam-Webster unabridged
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Time Traveler for linchpin
The first known use of linchpin was in the 13th century
See more words from the same century