/ Thesaurus / O Synonyms of on earth Find synonyms for: Adverb1. on earthusage: used with question words to convey surprise; "what on earth are you doing?"WordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: diaphanous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language