/ Dictionary / Index M myocardium: Meaning and Definition of Find definitions for: my•o•car•di•um Pronunciation: (mī"u-kär'dē-um), [key] — pl. -di•a the muscular substance of the heart. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: myocardium (Thesaurus) myocarditis myoclonia Related Content Daily Word Quiz: panacea Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language