The Collaborative International Dictionary
Thoroughpin
Thoroughpin \Thor"ough*pin`\, n. (Far.) A disease of the hock (sometimes of the knee) of a horse, caused by inflammation of the synovial membrane and a consequent excessive secretion of the synovial fluid; -- probably so called because there is usually an oval swelling on each side of the leg, appearing somewhat as if a pin had been thrust through.
Wiktionary
thoroughpin
n. An abnormal swelling (tenosynovitis) on the sides of the hock joint of horses