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):
untruthfully adv 1: in a mendacious and untruthful manner; "I told him, quite untruthfully, that I had just returned from leave" [syn: mendaciously, untruthfully] [ant: truthfully]