Source : Webster's Revised Unabridged Dictionary (1913)

Bridoon \Bri*doon"\, n. [F. bridon, from bride; of German
   origin. See {Bridle}, n.] (Mil.)
   The snaffle and rein of a military bridle, which acts
   independently of the bit, at the pleasure of the rider. It is
   used in connection with a curb bit, which has its own rein.
   --Campbell.

Source : WordNet®

bridoon
     n : a bit resembling a snaffle bit; used with a separate curb