/ Thesaurus / P Synonyms of plesiosaurus Find synonyms for: Noun1. plesiosaur, plesiosaurus, archosaur, archosaurian, archosaurian reptileusage: extinct marine reptile with a small head on a long neck a short tail and four paddle-shaped limbs; of the Jurassic and CretaceousWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: diaphanous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language