/ Thesaurus / S Synonyms of sound barrier Find synonyms for: Noun1. sonic barrier, sound barrier, drag, retarding forceusage: the increase in aerodynamic drag as an airplane approaches the speed of soundWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: labyrinth Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language