The Collaborative International Dictionary of English v.0.48:

Mantel \Man"tel\, n. [The same word as mantle a garment; cf. F.
   manteau de chemin['e]e. See Mantle.] (Arch.)
   The finish around a fireplace, covering the chimney-breast in
   front and sometimes on both sides; especially, a shelf above
   the fireplace, and its supports. The shelf is called also a
   mantelpiece or mantlepiece. [Written also mantle.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

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