Crupper

crupper
    n 1: a strap from the back of a saddle passing under the horse's
         tail; prevents saddle from slipping forward
    

Crupper \Crup"per\, v. t.
   To fit with a crupper; to place a crupper upon; as, to
   crupper a horse.
   [1913 Webster]
    

Crupper \Crup"per\ (kr?p"p?r in U.S.; kr?p"?r in Eng.), n. [F.
   croupi?re, fr. croupe. See {Croup} the rump of a horse.]
   [Written also {crouper}.]
   1. The buttocks or rump of a horse.
      [1913 Webster]

   2. A leather loop, passing under a horse's tail, and buckled
      to the saddle to keep it from slipping forwards.
      [1913 Webster]
    

59 Moby Thesaurus words for "crupper":
      back band, backside, backstrap, bearing rein, behind, bellyband,
      bit, blinders, blinds, breeching, bridle, butt, buttocks,
      caparison, cavesson, checkrein, cheekpiece, chinband, cinch,
      collar, croup, crownband, curb, gag swivel, girth, hackamore,
      halter, hames, hametugs, harness, haunches, headgear, headstall,
      hind end, hip straps, jaquima, jerk line, lines, martingale, nates,
      noseband, pole strap, posterior, rear, rear end, reins, ribbons,
      rump, saddle, shaft tug, side check, snaffle, surcingle, tack,
      tackle, trappings, tug, winker braces, yoke