D defs.my
Entry 1 sense Webster, 1913

Counteract

/(koun`t?r-?kt")/ · Coun·ter·act · IPA /ˈkaʊntəɹˌækt/
01 v. t. To act in opposition to; to hinder, defeat, or frustrate, by contrary agency or influence; as, to counteract the effect of medicines; to co…
imp. & p. p. Counteracted; p. pr. & vb. n. Counteracting
  1. 1.
    To act in opposition to; to hinder, defeat, or frustrate, by contrary agency or influence; as, to counteract the effect of medicines; to counteract good advice.