/ Dictionary / Index M mentum: Meaning and Definition of Find definitions for: men•tum Pronunciation: (men'tum), [key] — pl. -ta the medial plate of the labium in insects. a chinlike protuberance formed by the sepals and the base of the column in some orchids. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: mentum (Thesaurus) mentor menu Related Content Daily Word Quiz: morose Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language