/ Thesaurus / M Synonyms of main diagonal Find synonyms for: Noun1. main diagonal, principal diagonal, diagonalusage: the diagonal of a square matrix running from the upper left entry to the lower right entryWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: panacea Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language