The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Performing such inimitable feats.        --Cowper.
   -- In*im"i*ta*ble*ness, n. -- In*im"i*ta*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inimitably
    adv 1: in an unreproducible manner; "he has an inimitably
           verbose style" [syn: inimitably, unreproducibly]