Source : Webster's Revised Unabridged Dictionary (1913)

Brevet \Bre*vet"\ (br[-e]*v[e^]t"), v. t. [imp. & p. p.
   {Brevetted}; p. pr. & vb. n. {Brevetting}.] (Mil.)
   To confer rank upon by brevet.

Brevet \Bre*vet"\, a. (Mil.)
   Taking or conferring rank by brevet; as, a brevet colonel; a
   brevet commission.

Brevet \Bre*vet"\ (br[-e]*v[e^]t"; 277), n. [F. brevet, LL.
   brevetum, fr. L. brevis short. See {Brief}.]
   1. A warrant from the government, granting a privilege,
      title, or dignity. [French usage].

   2. (Mil.) A commission giving an officer higher rank than
      that for which he receives pay; an honorary promotion of
      an officer.

   Note: In the United States army, rank by brevet is conferred,
         by and with the advice and consent of the Senate, for
         ``gallant actions or meritorious services.'' A brevet
         rank gives no right of command in the particular corps
         to which the officer brevetted belongs, and can be
         exercised only by special assignment of the President,
         or on court martial, and detachments composed of
         different corps, with pay of the brevet rank when on
         such duty.

Source : WordNet®

brevet
     n : a document entitling a commissioned officer to hold a higher
         rank temporarily (but without higher pay)
     v : promote somebody by brevet, in the military
     [also: {brevetting}, {brevetted}]