Source : Webster's Revised Unabridged Dictionary (1913)

Chapeau \Cha`peau"\, n.; pl. {Chapeux}. [F., fr. OF. chapel hat.
   See {Chaplet}.]
   1. A hat or covering for the head.

   2. (Her.) A cap of maintenance. See {Maintenance}.

   {Chapeau bras}[F. chapeau hat + bras arm], a hat so made that
      it can be compressed and carried under the arm without
      injury. Such hats were particularly worn on dress
      occasions by gentlemen in the 18th century. A chapeau bras
      is now worn in the United States army by general and staff
      officers.