counteract /ˈkaʊntəɹˌækt/verb 2noun 1forms 3 verb2 •To have a contrary or opposing effect or force on someone or something. •To deliberately act in opposition to, to thwart or frustrate. noun1 •An action performed in opposition to another action.Every time there is a march by the Ku Klux Klan or a swastika painted on a Jewish building, there could be a counteract of reconciliation within twenty-four hours. — 2006 formscounteracted · counteracting · counteracts