The Collaborative International Dictionary of English v.0.48:

Cheyennes \Chey*ennes"\, n. pl.; sing. cheyenne. (Ethnol.)
   A warlike tribe of indians, related to the blackfeet,
   formerly inhabiting the region of Wyoming, but now mostly on
   reservations in the Indian Territory. They are noted for
   their horsemanship.
   [1913 Webster]