(v. t.) To act in opposition to; to hinder; as, to counteract the effect of medicines; to counteract good advice\.

annul antagonize baffle balance balk be antipathetic be at cross-purposes be inimical be opposed to beat against blast brave bump heads cancel cancel out challenge checkmate circumvent clash collide conflict conflict with confound confront confute contend contradict contrapose contraposit contrast contrast with contravene controvert correct counter counterattack counterbalance countercheck countermand counterpoise counterpose countervail counterweigh counterwork cross dash defeat defy destroy discomfit disconcert discountenance dish disrupt elude equiponderate face fix flummox foil front frustrate go against go counter to interfere with join the opposition juxtapose in opposition knock the chocks lie opposite lock horns match meet head-on militate against mitigate negate negative neutralize nonplus not abide nullify offset oppose oppugn perplex play at cross-purposes polarize pose against protest put in opposition rectify redress resist right ruin run against run counter to sabotage scotch set off set over against spike spoil square square up stand opposed stand opposite stonewall stump subtend swim upstream take issue with thwart traverse upset vote against withstand work against