Breadcrumb Home > Dictionary > Index M mainspring: Meaning and Definition of Find definitions for: main•spring Pronunciation: (mān'spring"), [key] — n. the principal spring in a mechanism, as in a watch. the chief motive power; the impelling cause. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: mainspring (Thesaurus) mainsheet mainstay TrendingHere are the facts and trivia that people are buzzing about. Biographies: Notable Jewish Religious Leaders Current Events This Week: September 2023 Hispanic Population and the 2010 U.S. Census 50 Spookiest Halloween Quotes Preamble of the United Nations Charter The Jewish Calendar ✖ Related Content Daily Word Quiz: factotum Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language