The Collaborative International Dictionary of English v.0.48:

Arrondissement \Ar`ron`disse`ment"\, n. [F., fr. arrondir to
   make round; ad + rond round, L. rotundus.]
   A subdivision of a department. [France]
   [1913 Webster]

   Note: The territory of France, since the revolution, has been
         divided into departments, those into arrondissements,
         those into cantons, and the latter into communes.
         [1913 Webster]