The Collaborative International Dictionary of English v.0.48:

Untruth \Un*truth"\, n.
   1. The quality of being untrue; contrariety to truth; want of
      veracity; also, treachery; faithlessness; disloyalty.
      --Chaucer.
      [1913 Webster]

   2. That which is untrue; a false assertion; a falsehood; a
      lie; also, an act of treachery or disloyalty. --Shak.
      [1913 Webster]

   Syn: Lie; falsehood. See Lie.
        [1913 Webster]

WordNet (r) 3.0 (2006):

untruth
    n 1: a false statement [syn: falsehood, falsity, untruth]
         [ant: true statement, truth]