The Collaborative International Dictionary of English v.0.48:

Identity \I*den"ti*ty\, n.; pl. Identities. [F. identit['e],
   LL. identitas, fr. L. idem the same, from the root of is he,
   that; cf. Skr. idam this. Cf. Item.]
   1. The state or quality of being identical, or the same;
      sameness.
      [1913 Webster]

            Identity is a relation between our cognitions of a
            thing, not between things themselves. --Sir W.
                                                  Hamilton.
      [1913 Webster]

   2. The condition of being the same with something described
      or asserted, or of possessing a character claimed; as, to
      establish the identity of stolen goods.
      [1913 Webster]

   3. (Math.) An identical equation.
      [1913 Webster]

WordNet (r) 3.0 (2006):

identity
    n 1: the distinct personality of an individual regarded as a
         persisting entity; "you can lose your identity when you
         join the army" [syn: identity, personal identity,
         individuality]
    2: the individual characteristics by which a thing or person is
       recognized or known; "geneticists only recently discovered
       the identity of the gene that causes it"; "it was too dark to
       determine his identity"; "she guessed the identity of his
       lover"
    3: an operator that leaves unchanged the element on which it
       operates; "the identity under numerical multiplication is 1"
       [syn: identity, identity element, identity operator]
    4: exact sameness; "they shared an identity of interests" [syn:
       identity, identicalness, indistinguishability]