Siouan languages
Authors who call the entire family "Siouan" distinguish the two branches as "Western Siouan" and "Eastern Siouan" or as "Siouan-proper" and "Catawban". Others restrict the name "Siouan" to the western branch and use the name "Siouan–Catawban" for the entire family. Generally, however, the name "Siouan" is used without distinction.
Sioux language
Sioux has three major regional varieties, with other sub-varieties:Yankton-Yanktonai (Western Dakota) stands between Santee-Sisseton (Eastern Dakota) and Lakota within the dialect continuum. It is phonetically closer to Santee-Sisseton but lexically and grammatically, it is much closer to Lakota. For this reason Lakota and Western Dakota are much more mutually intelligible than each is with Eastern Dakota. The assumed extent of mutual intelligibility is usually overestimated by speakers of the language. While Lakota and Yankton-Yanktonai speakers understand each other to a great extent, they each find it difficult to follow Santee-Sisseton speakers.