Sentence:  But when a board of inquiry was called to look into the charges of cowardice made against him , the men who had seen Reno leave the battlefield and the officer who had heard Reno suggest that the wounded be left to be tortured by the <WSD>Sioux</WSD> , refused to say a harsh word against him . 
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