LINCHPIN
linchpin, lynchpin
(noun) pin inserted through an axletree to hold a wheel on
anchor, mainstay, keystone, backbone, linchpin, lynchpin
(noun) a central cohesive source of support and stability; “faith is his anchor”; “the keystone of campaign reform was the ban on soft money”; “he is the linchpin of this firm”
Source: WordNet® 3.1
Etymology
Noun
linchpin (plural linchpins)
A pin inserted through holes at the end of an axle or shaft, so as to secure a wheel or shaft-mounted device.
(figuratively) A central cohesive source of stability and security; a person or thing that is critical to a system or organisation.
Usage notes
• Figurative use attested from the mid-20th century.
Source: Wiktionary
Linch"pin`, n. Etym: [AS. lynis the axletree; akin to D. luns
linchpin, OS. lunisa, LG. lunse, G. lĂĽnse, OHG. lun peg, bolt.]
Definition: A pin used to prevent the wheel of a vehicle from sliding off
the axletree.
Source: Webster’s Unabridged Dictionary 1913 Edition