The Collaborative International Dictionary of English v.0.48:
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
To attack by words or arguments; to contradict; to assail; to
call in question; to make insinuations against; to gainsay;
to oppose; as, to impugn a person's integrity.
The truth hereof I will not rashly impugn, or
overboldly affirm. --Peacham.