Sioux

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A member of a group of Native American peoples, comprising the Lakota, the Santee, the Yankton, and the Yanktonai, inhabiting the northern Great Plains from Minnesota to eastern Montana and from southern Saskatchewan to Nebraska. Present-day Sioux populations are located mainly in North and South Dakota, Minnesota, Montana, and Nebraska.
• noun Any of the Siouan languages of the Sioux peoples.

from The Century Dictionary.

• noun A member of a family of North American Indians, now confined chiefly to North Dakota, South Dakota, and parts of Wyoming, Nebraska, and Montana.
• Of or pertaining to the Sioux; Siouan; Dakotan: as, the Sioux wars; a Sioux village.

from the GNU version of the Collaborative International Dictionary of English.

• (Ethnol.) A nation of American Indians; see Dakotas.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun Name applied to various formerly nomadic Native American tribes of the North American Great Plains.
• proper noun The group of languages spoken by the Sioux.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a member of a group of North American Indian peoples who spoke a Siouan language and who ranged from Lake Michigan to the Rocky Mountains