/ Thesaurus / S Synonyms of subclass synapsida Find synonyms for: Noun1. Synapsida, subclass Synapsida, classusage: extinct reptiles of the Permian to Jurassic considered ancestral to mammalsWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: effervescent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language