The Collaborative International Dictionary of English v.0.48:

Bateau \Ba*teau"\, n.; pl. Bateaux. [F. bateau, LL. batellus,
   fr. battus, batus, boat, which agrees with AS. b[=a]t boat:
   cf. W. bad boat. See Boat, n.]
   A boat; esp. a flat-bottomed, clumsy boat used on the
   Canadian lakes and rivers. [Written also, but less properly,
   batteau.]
   [1913 Webster]

   Bateau bridge, a floating bridge supported by bateaux.
      [1913 Webster]