/ Dictionary / Index M meconium: Meaning and Definition of Find definitions for: me•co•ni•um Pronunciation: (mi-kō'nē-um), [key] — n. the first fecal excretion of a newborn child, composed chiefly of bile, mucus, and epithelial cells. fecal mass released at pupation by the larvae of some insects. the milky sap of the unripe seed pods of the opium poppy; crude opium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: meconium (Thesaurus) mecometer mecopteran Related Content Daily Word Quiz: pugilist Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language