The Collaborative International Dictionary of English v.0.48:

gateau \ga*teau"\, gateau \g[^a]*teau"\(g[.a]*t[=o]"), n. [F.
   cake.] (Cookery)
   Any of various rich and elaborate cakes, particularly a light
   sponge cake having a rich filling or rich icing, such as
   gateau foret noire (Black Forest Cake).
   [WordNet 1.5 +PJC]