linch‧pin ,
lynchpin /ˈlɪntʃˌpɪn/
noun[
Date: 1300-1400;
Origin: linch 'pin fastening a wheel to an axle' (11-16 centuries) (from Old English lynis) + pin]
the linchpin of something the person or thing in a group, system etc that is most important, because everything depends on them
[TahlilGaran] Dictionary of Contemporary English ▲