Word Origin & History
group of N.Amer. Indian tribes, 1761, from N.Amer. Fr., aphetic for Nadouessioux, sometimes said to be from Ojibway (Algonquian) Natowessiwak (pl.), lit. "little snakes," from nadowe "Iroquois" (lit. "big snakes"). Another explanation traces it to early Ottawa (Algonquian) sing. /na:towe:ssi/ (pl. /na:towe:ssiwak/)
"Sioux," apparently from a verb meaning "to speak a foreign language" [Bright]. In either case, a name given by their neighbors; the people's name for themselves is Dakota, lit. "allies."