Source : Webster's Revised Unabridged Dictionary (1913)

Untruthful \Un*truth"ful\, a.
   Not truthful; unveracious; contrary to the truth or the fact.
   -- {Un*truth"ful*ly}, adv. -- {Un*truth"ful*ness}, n.

Source : WordNet®

untruthful
     adj : not expressing or given to expressing the truth; "the
           statement given under oath was untruthful"; "an
           untruthful person" [ant: {truthful}]