The Collaborative International Dictionary of English v.0.48:

Coteau \Co`teau"\, n.; pl. Coteaux. [F., a hill.] [Canada & U.
   S.]
   1. A hilly upland including the divide between two valleys; a
      divide.
      [Webster 1913 Suppl.]

   2. The side of a valley.
      [Webster 1913 Suppl.]