The Collaborative International Dictionary
crouper
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.]
The buttocks or rump of a horse.
A leather loop, passing under a horse's tail, and buckled to the saddle to keep it from slipping forwards.
Wiktionary
crouper
n. (obsolete form of crupper English)