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®

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