/ Thesaurus / C Synonyms of co2 Find synonyms for: Noun1. carbon dioxide, CO2, carbonic acid gas, dioxide, greenhouse gas, greenhouse emissionusage: a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesisWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: reticent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language