Synonyms for Siouan (same or very similar meaning)
WordNet sense 1 (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):
SiouxWordNet sense 2 (a family of North American Indian languages spoken by the Sioux):
Siouan languageFrom the ODE community, based on WordNetadd/edit