/ Thesaurus / I Synonyms of in theory Find synonyms for: Adverb1. in principle, in theory, in essenceusage: with regard to fundamentals although not concerning details; "in principle, we agree"WordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: penury Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language