Sentence:  But eager as Kate was for her <WSD>beauty sleep</WSD>, the light burned late in her room. 
Meaning of the word marked with <WSD> tags:  Sleep before midnight, on the belief that early sleep hours conduce to health and beauty.<ref>John Stephen Farmer and William Ernest Henley, "Slang and Its Analogues Past and Present" (1890), [https://books.google.com/books?id=CbATAAAAQAAJ&pg=159&q=beauty-sleep p. 159].</ref>