Webster’s Revised Unabridged Dictionary · 1913
Crupper
Crup′per (kr?p′p?r in U.S.; kr?p′?r in Eng.), n. [F. croupière, fr. croupe. See Croup the rump of a horse.] [Written also crouper.] 1. The buttocks or rump of a horse.
2. A leather loop, passing under a horse's tail, and buckled to the saddle to keep it from slipping forwards.
Crup′per, v. t. To fit with a crupper; to place a crupper upon; as, to crupper a horse.