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]