Cay·use 
(kī-ys, kīys′)
(kī-ys, kīys′)n. pl. Cayuse or Cay·us·es
1. A member of a Native American people inhabiting northeast Oregon and southeast Washington.
2.
a. The extinct traditional language of the Cayuse, not closely related to any other.
b. The dialect of Nez Perce spoken by the Cayuse in the 1800s and 1900s.
[From Columbian Salish (Salish language of the Columbia River valley) qayús, Cayuse or a kindred word in another language of the Pacific Northwest .]