/ Dictionary / Index U USMC: Meaning and Definition of Find definitions for: USMC Pronunciation: [key] United States Marine Corps. United States Maritime Commission. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: usmc (Thesaurus) U.S.M.A. USMS Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language