Other forms: linchpins
A linchpin is the pin that holds a wheel on, or the vital element. Pull the linchpin, the linchpin of the plan, he was the linchpin.
The literal one is a small pin through the axle, and losing it loses the wheel — which is exactly why the metaphor is so strong. Calling somebody the linchpin says everything depends on them, and it is high praise and a warning at once.
1nounlinchpinThe pin that holds a wheel on, or the vital element.
“As the team's best player, she is the linchpin of the whole defence.”
linchpin is a pin, or an essential.
Middle English lynspin, from Old English lynis, an axle, plus pin.
Proto-Germanic
*lunaz
Proto-West Germanic
*lunis
Old English
lynis — lynchpin
Middle English
lynspin
English, today
linchpin
Built from
From Middle English lynspin, compound of lins (“axletree”) and pin, from Old English lynis (“lynchpin”), from Proto-West Germanic lunis, from Proto-Germanic lunaz – compare German Lünse and Dutch luns – from Proto-Indo-European -. Possible further cognates are Welsh olwyn (“wheel”), xcl ողն (“back; spine, backbone”) and Sanskrit आणि (“lynchpin”). Figurative use attested from the mid-20th century.
Etymology from Wiktionary, CC BY-SA