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]

Moby Thesaurus II by Grady Ward, 1.0:

158 Moby Thesaurus words for "falsity":
   Punic faith, aberrancy, aberration, acting, affectation,
   appearance, attitudinizing, bad faith, barratry, blague, bluff,
   bluffing, breach of faith, breach of promise, breach of trust,
   canard, casuistry, cheating, cock-and-bull story, color, coloring,
   deceit, deceitfulness, deception, deceptiveness, defectiveness,
   delusion, dereliction, deviancy, disaffection, disguise,
   dishonesty, disingenuousness, disloyalty, dissemblance,
   dissembling, dissimulation, distortion, errancy, erroneousness,
   error, exaggeration, fabrication, facade, face, fairy tale,
   faithlessness, fake, fakery, faking, fallaciousness, fallacy,
   false air, false front, false show, falsehood, falseness,
   farfetched story, farrago, fault, faultiness, feigning, feint, fib,
   fickleness, fiction, fish story, flam, flaw, flawedness, flimflam,
   four-flushing, fraud, fraudulence, front, ghost story, gilt, gloss,
   half-truth, hamartia, heresy, heterodoxy, humbug, humbuggery,
   hypocrisy, illusion, imposture, inconstancy, infidelity,
   insincerity, inveracity, legal fiction, lie, little white lie,
   mala fides, masquerade, mendaciousness, mendacity,
   meretriciousness, misapplication, misconstruction, misdoing,
   misfeasance, misinterpretation, misjudgment, misrepresentation,
   ostentation, outward show, peccancy, perfidiousness, perfidy,
   perversion, pious fiction, playacting, pose, posing, posture,
   pretense, pretension, pretext, prevarication, recreancy,
   representation, seeming, self-contradiction, semblance, sham, show,
   simulacrum, simulation, sin, sinfulness, slight stretching,
   speciousness, spuriousness, story, tale, tall story, tall tale,
   taradiddle, trothlessness, trumped-up story, truthlessness,
   uncandidness, unfaith, unfaithfulness, unloyalty, unorthodoxy,
   unsteadfastness, untrueness, untruth, untruthfulness, varnish,
   white lie, window dressing, wrong, wrongness, yarn