Source : Webster's Revised Unabridged Dictionary (1913)

Inimitable \In*im"i*ta*ble\, a. [L. inimitabilis: cf. F.
   inimitable. See {In-} not, and {Imitable}.]
   Not capable of being imitated, copied, or counterfeited;
   beyond imitation; surpassingly excellent; matchless;
   unrivaled; exceptional; unique; as, an inimitable style;
   inimitable eloquence. ``Inimitable force.'' --Dryden.

         Performing such inimitable feats.        --Cowper.
   -- {In*im"i*ta*ble*ness}, n. -- {In*im"i*ta*bly}, adv.

Source : WordNet®

inimitable
     adj : defying imitation; matchless; "an inimitable style"