/ Thesaurus / C Synonyms of cantus firmus Find synonyms for: Noun1. cantus firmus, plainsong, plainchant, Gregorian chantusage: a melody used as the basis for a polyphonic compositionWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: acerbity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language