/ Thesaurus / A Synonyms of atomic number 18 Find synonyms for: Noun1. argon, Ar, atomic number 18, chemical element, element, noble gas, inert gas, argononusage: a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphereWordNet 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