Sentence:  "Yes, let 'Sister' Davis have a whack at it too," urged George Bland. Tom Davis, who was Joe Matson's particular chum, was <WSD>designated</WSD> "Sister" because, in an incautious moment, when first coming to Excelsior Hall, he had shown a picture of his very pretty sister, Mabel. 
Meaning of the word marked with <WSD> tags:  To call by a distinctive title; to name.