/ Dictionary / Index M magnum opus: Meaning and Definition of Find definitions for: mag'num o'pus Pronunciation: [key] a great work, esp. the chief work of a writer or artist:Remembrance of Things Past. Proust's magnum opus is Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. magnum Magnus Annus* Related Content Daily Word Quiz: vernacular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language