Cayuse (kĪyōsˈ) [key], Native North Americans who formerly occupied parts of NE Oregon and SE Washington. They were closely associated with the Nez Percé and spoke a language belonging to the Sahaptin-Chinook branch of the Penutian linguistic stock (see Native American Languages). A mission was established (1836) among them by Marcus Whitman at Waiilatpu. In 1847 the Cayuse, blaming the missionaries for an outbreak of smallpox, attacked the mission and killed the Whitmans and their helpers. The settlers then declared war and defeated the Cayuse. In 1855 they were placed on the Umatilla Reservation in Oregon, which they continue to share with the Wallawalla and Umatilla peoples; by 1990 they were among the smallest groups of Native Americans, numbering 126. A small horse bred by them gave the name cayuse to all Native American horses (see mustang).
See R. H. Ruby and J. A. Brown, The Cayuse Indians (1972).
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