/ Dictionary / Index C counteract: Meaning and Definition of Find definitions for: coun•ter•act Pronunciation: (koun"tur-akt'), [key] — v.t. to act in opposition to; frustrate by contrary action. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: counteract (Thesaurus) counter counterargument Related Content Daily Word Quiz: sumptuous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language