/ Dictionary / Index D diagonal matrix: Meaning and Definition of Find definitions for: diag'onal ma'trix Pronunciation: [key] — Math. Math. a square matrix in which all the entries except those along the diagonal from upper left to lower right are zero. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. diagonalize diagram Related Content Daily Word Quiz: rustic Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language