/ Dictionary / Index M mental illness: Meaning and Definition of Find definitions for: men'tal ill'ness Pronunciation: [key] any of the various forms of psychosis or severe neurosis. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mental health mentalism Related Content Daily Word Quiz: placid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language