The Collaborative International Dictionary of English v.0.48:

Falsity \Fal"si*ty\, n.;pl. Falsities. [L. falsitas: cf. F.
   fausset['e], OF. also, falsit['e]. See False, a.]
   1. The quality of being false; coutrariety or want of
      conformity to truth.
      [1913 Webster]

            Probability does not make any alteration, either in
            the truth or falsity of things.       --South.
      [1913 Webster]

   2. That which is false; falsehood; a lie; a false assertion.
      [1913 Webster]

            Men often swallow falsities for truths. --Sir T.
                                                  Brown.

   Syn: Falsehood; lie; deceit.

   Usage: Falsity, Falsehood, Lie. Falsity denotes the
          state or quality of being false. A falsehood is a
          false declaration designedly made. A lie is a gross,
          unblushing falsehood. The falsity of a person's
          assertion may be proved by the evidence of others and
          thus the charge of falsehood be fastened upon him.
          [1913 Webster]

WordNet (r) 3.0 (2006):

falsity
    n 1: the state of being false or untrue; "argument could not
         determine its truth or falsity" [syn: falsity,
         falseness] [ant: the true, trueness, truth,
         verity]
    2: a false statement [syn: falsehood, falsity, untruth]
       [ant: true statement, truth]