The Collaborative International Dictionary of English v.0.48:

Ambiguity \Am`bi*gu"i*ty\, n.; pl. Ambiguities. [L.
   ambiguitas, fr. ambiguus: cf. F. ambiguit['e].]
   The quality or state of being ambiguous; doubtfulness or
   uncertainty, particularly as to the signification of
   language, arising from its admitting of more than one
   meaning; an equivocal word or expression.
   [1913 Webster]

         No shadow of ambiguity can rest upon the course to be
         pursued.                                 --I. Taylor.
   [1913 Webster]

         The words are of single signification, without any
         ambiguity.                               --South.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ambiguity
    n 1: an expression whose meaning cannot be determined from its
         context
    2: unclearness by virtue of having more than one meaning [syn:
       ambiguity, equivocalness] [ant: unambiguity,
       unequivocalness]

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "ambiguity":
   Janus, ambivalence, amphibologism, amphibology, amphiboly,
   antinomy, asymmetry, biformity, bifurcation, cavil, conjugation,
   counterword, dichotomy, disproportion, disproportionateness, dodge,
   double entendre, double meaning, double-talk, doubleness,
   doublethink, doubling, dualism, duality, duplexity, duplication,
   duplicity, equivocacy, equivocal, equivocality, equivocalness,
   equivocation, equivoque, evasion, haggling, hair-splitting,
   halving, hedge, heresy, heterodoxy, heterogeneity, impenetrability,
   imprecision, inapprehensibility, inarticulateness, incognizability,
   incoherence, incommensurability, incompatibility,
   incomprehensibility, inconclusiveness, incongruity, inconsistency,
   inconsonance, indefiniteness, indistinctness, inscrutability,
   irony, irreconcilability, nonconformability, nonconformity,
   numinousness, obscurity, oxymoron, pairing, paradox, polarity,
   polysemant, polysemousness, portmanteau word, pun, quibbling,
   ramblingness, self-contradiction, shift, squinting construction,
   subterfuge, tergiversation, twinning, two-facedness, twoness,
   uncertainty, unconformability, unconformity, unconnectedness,
   unfathomableness, unintelligibility, unknowability, unorthodoxy,
   unsearchableness, vagueness, weasel word



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

AMBIGUITY, contracts, construction. When au expression has been used in an
instrument of writing which may be understood in more than one sense, it is
said there is an ambiguity,
     2. There are two sorts of ambiguities of words, ambiguitas latens and
ambiguitas patens.
     3. The first occurs when the deed or instrument is sufficiently certain
and free from ambiguity, but the ambiguity is produced by something
extrinsic, or some collateral matter out of the instrument; for example, if
a man devise property to his cousin A B, and he has two cousins of that
name, in such case parol evidence will be received to explain the ambiguity.
     4. The second or patent ambiguity occurs when a clause in a deed, will,
or other instrument, is so defectively expressed, that a court of law, which
has to put a construction on the instrument, is unable to collect the
intention of the party. In such case, evidence of the declaration of the
party cannot be submitted to explain his intention, and the clause will be
void for its uncertainty. In Pennsylvania, this rule is somewhat qualified.
3 Binn. 587; 4 Binn. 482. Vide generally, Bac. Max. Reg. 23; 1 Phu. Ev. 410
to 420; 3 Stark. Ev. 1021 ; I Com. Dig. 575; Sudg. Vend. 113. The civil law
on this subject will be found in Dig. lib. 50, t. 17, 1. 67; lib. 45, t. 1,
1. 8; and lib. 22, t. 1, 1. 4.