Source : Webster's Revised Unabridged Dictionary (1913)

Impugn \Im*pugn"\, v. t. [imp. & p. p. {Impugned}; p. pr. & vb.
   n. {Impugning}.] [OE. impugnen, F. impugner, fr. L.
   impugnare; in on, against + pugnare to flight. See
   {Pugnacious}.]
   To attack by words or arguments; to contradict; to assail; to
   call in question; to make insinuations against; to gainsay;
   to oppose.

         The truth hereof I will net rashly pugn, or overboldly
         affirm.                                  --Peacham.

Source : WordNet®

impugn
     v : attack as false or wrong