Source : Webster's Revised Unabridged Dictionary (1913)

Brumaire \Bru`maire"\, n. [F., fr. L. bruma winter.]
   The second month of the calendar adopted by the first French
   republic. It began thirty days after the autumnal equinox.
   See {Vendemiaire}.

Source : WordNet®

Brumaire
     n : second month of the Revolutionary calendar (October and
         November); the month of mist