Cayuse is an archaic term used in the American west, usually referring to a feral or low-quality horse or pony.
In British Columbia, the variant word cayoosh refers to a particular breed of mountain pony with shorter legs and large hindquarters, typically also of Indian husbandry.
The origin of the word is a Native American adaptation of the Spanish caballo, with the -s ending a noun form in Salishan languages. A variant adaptation, kiuatan, with a Sahaptian -tan ending, is the main word for "horse" or "pony" in the Chinook Jargon, although cayuse or cayoosh was also used in some areas. For this reason, some horses owned by Native American people were dubbed "cayuse," often with derogatory intent.