/ Thesaurus / S Synonyms of side effect Find synonyms for: Noun1. side effect, effectusage: a secondary and usually adverse effect of a drug or therapy; "severe headaches are one of the side effects of the drug"2. side effect, fallout, consequence, effect, outcome, result, event, issue, upshotusage: any adverse and unwanted secondary effect; "a strategy to contain the fallout from the accounting scandal"WordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: denizen Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language