/ Thesaurus / C Synonyms of co sign Find synonyms for: Verb1. co-sign, cosign, validate, formalize, formaliseusage: sign jointly; "Husband and wife co-signed the lease"2. cosign, co-sign, endorse, indorseusage: sign and endorse (another person's signature), as for a loanWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: devout Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language