linchpin

• lynchpin

From Middle English lynspin, compound of lins (“axletree”) and pin, from Old English lynis (“lynchpin”), from Proto-Germanic *lunaz (compare German Lünse), from Proto-Indo-European (compare Welsh olwyn (“wheel”), Old Armenian ողն (ołn, “back; spine, backbone”), Sanskrit आणि (āṇí, “lynchpin”)). Figurative use attested from the mid-20th century.

linchpin (plural linchpins)

1. A pin inserted through holes at the end of an axle, so as to secure a wheel.
   • 1864 June 1, Baily's Magazine of Sports & Pastimes, volume 8, page 110:

     Every design that villany could suggest was had recourse to in the hopes of nobbling Wild Dayrell; but never being left for an hour by either his trainer or jockey, he escaped the intended “coopering,” even when the lynchpins of the wheels of his van had been tampered with.

2. (figuratively) A central cohesive source of stability and security; a person or thing that is critical to a system or organisation.
   • 1958, The Eastern Economist:

     What is difficult to appreciate, however, is the discrepancy between his statement to the 'Manchester Guardian' correspondent and his known abhorance for party politics, which is the lynchpin of modern democracy.

   • 2013, Dvaid Sines, Community and Public Health Nursing, page 2006:

     Community nurses have been described as the lynchpins of palliative care in the community.