Macro-Siouan languages
In the 19th century, Robert Latham suggested that the Siouan languages are related to the Caddoan and Iroquoian languages. In 1931, Louis Allen presented the first list of systematic correspondences between a set of 25 lexical items in Siouan and Iroquoian. In the 1960s and 1970s, Wallace Chafe further explored the link between Siouan and Caddoan languages. In the 1990s, Marianne Mithun compared the morphology and syntax of all the three families. At present, the Macro-Siouan hypothesis based on relations among Siouan, Caddoan, and Iroquoian is not universally accepted as proven.
Sioux
The name "Sioux" was adopted in English by the 1760s from French. It is abbreviated from "Nadouessioux", first attested by Jean Nicolet in 1640. The name is sometimes said to be derived from an Ojibwe exonym for the Sioux meaning "little snakes" (compare "nadowe" "big snakes", used for the Iroquois). The spelling in "-x" is due to the French plural marker.
The Proto-Algonquian form "*na·towe·wa", meaning "Northern Iroquoian", has reflexes in several daughter languages that refer to a small rattlesnake (massasauga, "Sistrurus"). An alternative explanation is derivation from an (Algonquian) exonym " na·towe·ssiw" (plural " na·towe·ssiwak"), from a verb "*-a·towe·" meaning "to speak a foreign language". The current Ojibwe term for the Sioux and related groups is "Bwaanag" (singular "Bwaan"), meaning "roasters". Presumably, this refers to the style of cooking the Sioux used in the past.