mainspring

[ meyn-spring ]
/ ˈmeɪnˌsprɪŋ /

noun

the principal spring in a mechanism, as in a watch.
the chief motive power; the impelling cause.

Origin of mainspring

First recorded in 1585–95; main1 + spring
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for mainspring

British Dictionary definitions for mainspring

mainspring

/ (ˈmeɪnˌsprɪŋ) /

noun

the principal power spring of a mechanism, esp in a watch or clock
the chief cause or motive of something

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012