The Collaborative International Dictionary of English v.0.48:

Chimney-piece \Chim"ney-piece`\, chimneypiece \chimneypiece\, n.
   (Arch.)
   A decorative construction around the opening of a fireplace;
   also, the shelf that projects from wall above fireplace;
   mantlepiece. [Chiefly Brit.]

   Syn: mantel, mantelpiece, mantle, mantlepiece.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

chimneypiece
    n 1: shelf that projects from wall above fireplace; "in Britain
         they call a mantel a chimneypiece" [syn: mantel,
         mantelpiece, mantle, mantlepiece, chimneypiece]