The Collaborative International Dictionary of English v.0.48:

Unique \U*nique"\, a. [F. unique; cf. It. unico; from L. unicus,
   from unus one. See One.]
   Being without a like or equal; unmatched; unequaled;
   unparalleled; single in kind or excellence; sole. --
   U*nique"ly, adv. -- U*nique"ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

uniqueness
    n 1: the quality of being one of a kind; "that singularity
         distinguished him from all his companions" [syn:
         singularity, uniqueness]