Sentence:  In September 1817 at Fort Daer ( Pembina ) Dickson met the noble lord whom , with the help of a band of <WSD>Sioux</WSD> , he escorted to Prairie du Chien . 
Meaning of the word marked with <WSD> tags:  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