Western Siouan languages
The Western Siouan languages, also called Siouan proper or simply Siouan, are a large language family native to North America. They are closely related to the Catawban languages, sometimes called Eastern Siouan, and together with them constitute the Siouan (Siouan–Catawban) language family.
Mandan
The Mandan language or "Nų́ų́ʔetaa íroo" belongs to the Siouan language family. It was initially thought to be closely related to the languages of the Hidatsa and the Crow. However, since the Mandan language has been in contact with Hidatsa and Crow for many years, the exact relationship between Mandan and other Siouan languages (including Hidatsa and Crow) has been obscured. For this reason, linguists classify Mandan most often as a separate branch of the Siouan family.