/ Thesaurus / S Synonyms of sign in Find synonyms for: Verb1. check in, sign in, reportusage: announce one's arrival, e.g. at hotels or airportsWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language