Source : Webster's Revised Unabridged Dictionary (1913)

Masterpiece \Mas"ter*piece`\, n.
   Anything done or made with extraordinary skill; a capital
   performance; a chef-d'[oe]uvre; a supreme achievement.

         The top and masterpiece of art.          --South.

         Dissimulation was his masterpiece.       --Claredon.

Source : WordNet®

masterpiece
     n 1: the most outstanding work of a creative artist or craftsman
          [syn: {chef-d'oeuvre}]
     2: an outstanding achievement