The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

untruthful
    adj 1: not expressing or given to expressing the truth; "the
           statement given under oath was untruthful"; "an
           untruthful person" [ant: true, truthful]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "untruthful":
   artful, calculating, crafty, deceitful, deceptive, delusive,
   delusory, dishonest, disingenuous, equivocal, false, falsehearted,
   forsworn, inaccurate, incorrect, insincere, knavish, lying,
   mendacious, misleading, perjured, prevaricating, roguish, scheming,
   shifty, truthless, uncandid, unfrank, unsincere, unveracious,
   wrong