The Collaborative International Dictionary of English v.0.48:

Cornice \Cor"nice\ (k?r"n?s), n. [F. corniche, It. cornice, LL.
   coronix, cornix, fr. L. coronis a curved line, a flourish
   with the pen at the end of a book or chapter, Gr. ???; akin
   to L. corona crown. sEE Crown, and cf. Coronis.] (Arch.)
   Any horizontal, molded or otherwise decorated projection
   which crowns or finishes the part to which it is affixed; as,
   the cornice of an order, pedestal, door, window, or house.
   --Gwilt.
   [1913 Webster]

   Cornice ring, the ring on a cannon next behind the muzzle
      ring.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cornice
    n 1: a decorative framework to conceal curtain fixtures at the
         top of a window casing [syn: cornice, valance, valance
         board, pelmet]
    2: a molding at the corner between the ceiling and the top of a
       wall
    3: the topmost projecting part of an entablature
    v 1: furnish with a cornice