linchpin

Meanings

1. 1
   noun

   a person or thing essential to the stability or success of a system or plan

   Reliable transport is the linchpin of the region's emergency plan.

2. 2
   noun

   a pin fitted through the end of an axle to keep a wheel in place

   The driver checked the linchpin before taking the cart onto the road.

From Middle English lynspin, combining lins, 'axletree,' with pin; lins descends from Old English lynis, 'linchpin.' The literal pin keeps a wheel on its axle. The now-common figurative sense, an indispensable source of stability, is attested from the mid-twentieth century.

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