What is Brevet?

Legal Definition
In France, a brevet is a warrant granted by the government to authorize an individual to do something for his own benefit, as a brevet d'invention, is a patent to secure a man a right as inventor.

2. In our army, it signifies a commission conferring on an officer a degree of rank immediately above the one which he holds in his particular regiment, without, however conveying a right to receive a corresponding pay.
-- Bouviers Law Dictionary
Legal Definition
In military law. A commission by which an officer is promoted to the next higher rank, but without conferring a right to a corresponding increase of Pay. In French law. A privilege or warrant granted by the government to a private person, authorizing him to take a special benefit or exercise an exclusive privilege. Thus a brevet d'invention is a patent for an invention
-- Black's Law Dictionary