Counteract \Coun`ter*act"\ (koun`t?r-?kt"), v. t. [imp. & p. p.
{Counteracted}; p. pr. & vb. n. {Counteracting}.]
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.
[1913 Webster]