/ Dictionary / Index M mcg: Meaning and Definition of Find definitions for: mcg Pronunciation: [key] microgram. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: mcg (Thesaurus) McFee McGovern 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