/ Thesaurus / X Synonyms of xxi Find synonyms for: Noun1. twenty-one, 21, XXI, large integerusage: the cardinal number that is the sum of twenty and oneAdjective1. twenty-one, 21, xxi, cardinal (vs. ordinal)usage: being one more than twentyWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: feline Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language