/ Dictionary / Index G G.C.M.: Meaning and Definition of Find definitions for: G.C.M. Pronunciation: [key] greatest common measure. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. G clef GCR Related Content Daily Word Quiz: cetacean Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language