Linchpin

WORD OF THE DAY

linchpin / noun / LINCH-pin

Definition
1: a locking pin inserted crosswise (as through the end of an axle or shaft)
2: one that serves to hold together parts or elements that exist or function as a unit

Examples
Investors are betting that the new product line will be the linchpin that secures the company's place in the very competitive market in the years and decades to come.

"Saudi Arabia planned to take its giant oil company, Saudi Aramco, to the public markets. It was to be the linchpin of a grand economic vision, generating billions of dollars to pay for future-proofing the kingdom's economy, including huge investments in technology."
— Michael J. de la Merced, The New York Times, 25 Aug. 2018

Did You Know?
In his 1857 novel, Tom Brown's School Days, Thomas Hughes describes the "cowardly blackguard custom" of "taking the linch-pins out of the farmers' and bagmens' gigs at the fairs."
The linchpin in question held the wheel on the gig and removing it made it likely that the wheel would come off as the vehicle moved.
Such a pin was called a lynis in Old English; Middle English speakers added pin to form lynspin. By the early 20th century, English speakers were using linchpin for anything as critical to a complex situation as a linchpin is to a wagon, as when Winston Churchill, in 1930, wrote of Canada and the role it played in the relationship between Great Britain and the United States, that "no state, no country, no band of men can more truly be described as the linchpin of peace and world progress."