The Collaborative International Dictionary of English v.0.48:

Falsehood \False"hood\, n. [False + -hood]
   1. Want of truth or accuracy; an untrue assertion or
      representation; error; misrepresentation; falsity.
      [1913 Webster]

            Though it be a lie in the clock, it is but a
            falsehood in the hand of the dial when pointing at a
            wrong hour, if rightly following the direction of
            the wheel which moveth it.            --Fuller.
      [1913 Webster]

   2. A deliberate intentional assertion of what is known to be
      untrue; a departure from moral integrity; a lie.
      [1913 Webster]

   3. Treachery; deceit; perfidy; unfaithfulness.
      [1913 Webster]

            Betrayed by falsehood of his guard.   --Shak.
      [1913 Webster]

   4. A counterfeit; a false appearance; an imposture.
      [1913 Webster]

            For his molten image is falsehood.    --Jer. x. 14.
      [1913 Webster]

            No falsehood can endure
            Touch of celestial temper.            --Milton.

   Syn: Falsity; lie; untruth; fiction; fabrication. See
        Falsity.
        [1913 Webster]

WordNet (r) 3.0 (2006):

falsehood
    n 1: a false statement [syn: falsehood, falsity, untruth]
         [ant: true statement, truth]
    2: the act of rendering something false as by fraudulent changes
       (of documents or measures etc.) or counterfeiting [syn:
       falsification, falsehood]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "falsehood":
   blague, canard, cock-and-bull story, credibility gap, deceit,
   dishonesty, dissimulation, distortion, erroneousness, error,
   exaggeration, fabrication, fairy tale, fakery, fallaciousness,
   fallacy, falseness, falsity, farfetched story, farrago, feigning,
   fib, fibbery, fibbing, fiction, fish story, flam, flimflam, fraud,
   ghost story, half-truth, inveracity, legal fiction, lie,
   little white lie, lying, mendaciousness, mendacity,
   misrepresentation, misstatement, mythomania, pious fiction,
   pretense, prevarication, pseudology, sham, slight stretching,
   story, tale, tall story, tall tale, taradiddle, trumped-up story,
   truthlessness, untrueness, untruth, untruthfulness,
   unveraciousness, white lie, yarn



Bouvier's Law Dictionary, Revised 6th Ed (1856):

FALSEHOOD. A willful act or declaration contrary to truth. It is committed
either by the willful act of the party, or by dissimulation, or by words. It
is willful, for example, when the owner of a thing sells it twice, by
different contracts to different individuals, unknown to them; for in this
the seller must willfully declare the thing is his own, when he knows that it

is not so. It is committed by dissimulation when a creditor, having an
understanding with his former debtor, sells the land of the latter, although
he has been paid the debt which was due to him.
     2. Falsehood by word is committed when a witness swears to what he
knows not to be true. Falsehood is usually attendant on crime. Roscoe, Cr.
Ev. 362.
     3. A slander must be false to entitle the plaintiff to recover damages.
But whether a libel be true or false the writer or publisher may be indicted
for it. Bul N. P. 9; Selw. N. P. 1047, note 6; 5 Co. 125; Hawk. B. 1, c.
73, s. 6. Vide Dig. 48, 10, 31; Id. 22, 6, 2; Code, 9, 22, 20.
     4. It is a general rule, that if a witness testifies falsely as to any
one material fact, the whole of his testimony must be rejected but still the
jury may consider whether the wrong statement be of such character, as to
entitle the witness to be believed in other respects. 5 Shepl. R. 267. See
Lie.