The Great Sioux Nation
When talking about "the Sioux" it is important to understand that this single word applies to several different tribal peoples, not a single homogenous group. The word "Sioux" comes from the Chippewa word for 'snake' or 'enemy', since the two tribes were enemies. Although the Sioux's place in the history of the United States deals with their occupation of the Black Hills of South Dakota, the Sioux themselves were bands displaced from the Northeast when the British gave guns to the hostile Ojibwa. The Sioux eventually settled in the Black Hills, displacing the Cheyenne and Kiowa tribes who had occupied the hills previously. (nativeamericans.com)
The Sioux consist of seven different tribes, divided into three major groups. The Santee, or 'Dakota' group of Sioux which occupied the easternmost of the Sioux territories contained the Wahpekute, Mdewakantonwan, Wahpetonwan, and Sisitonwan tribes. The Nakota group occupied the central area of Sioux territories and consists of the Yankton and Yanktonai tribes. And the Teton tribe, also called the Lakota, occupied the western Sioux territories. After the move to the plains from their Northeastern home, the Teton tribe further subdivided into seven sub-bands, including the Hunkpapa, Sihasapa (Blackfoot), and Oglala Sioux, among others. (nativeamericans.com)
In Sioux, the names of the three groups, the Lakota, the Nakota, and the Dakota, all translate roughly to "friends" or "friendly". Although the Sioux were not originally native to the Black Hills, or Paha Sapa as they are called in the Sioux dialects, the Black Hills quickly became central to their survival within the Great Plains. The Paha Sapa also became mythically identified as sacred land, with spiritual significance as the place where humanity first emerged from the earth. (bbc.co.uk)