The Collaborative International Dictionary of English v.0.48:

Mousse \Mousse\ (m[=oo]s), n. [F.]
   1. (Cookery) A frozen dessert of a frothy texture, made of
      sweetened and flavored whipped cream, sometimes with the
      addition of egg yolks and gelatin. Mousse differs from ice
      cream in being beaten before -- not during -- the freezing
      process.
      [Webster 1913 Suppl.]

   2. Any of a variety of foods whipped to a light texture; as,
      a salmon mousse.
      [PJC]

   3. A foam containing special chemicals, used for styling
      hair.
      [PJC]

WordNet (r) 3.0 (2006):

mousse
    n 1: a rich, frothy, creamy dessert made with whipped egg whites
         and heavy cream
    2: a light creamy dish made from fish or meat and set with
       gelatin
    3: toiletry consisting of an aerosol foam used in hair styling
       [syn: mousse, hair mousse, hair gel]
    v 1: apply a styling gel to; "she mousses her hair" [syn:
         mousse, gel]