/ Dictionary / Index S supplementary angle: Meaning and Definition of Find definitions for: sup'plemen'tary an'gle Pronunciation: [key] — Math. Math. either of two angles that added together produce an angle of 180°. Cf. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. supplementary supplementary story Related Content Daily Word Quiz: paradox Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language