a member of any of the North American Indian peoples formerly inhabiting the Great Plains: they were of various linguistic stocks but shared certain cultural traits, such as the nomadic following of bison herds
See Plains Indian in American Heritage Dictionary 4
(plānz)
noun
A member of any of the Native American peoples inhabiting the Great Plains of the United States and Canada. The Plains Indians spoke a variety of unrelated languages but shared certain cultural features such as nomadic buffalo hunting, the use of conical tepees, and a reliance on the horse in hunting and warfare.