What does "chapeau" mean?

Chapeau: (Her.) A cap of maintenance. See Maintenance. Chapeau bras ( Etym: [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.

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