The term 'overnight visitor' can be summarized by the crossword solution 'Sandman', which is a seven-letter word. Sandman is a mythical figure in many cultures who is said to bring good dreams to children while they sleep. He is often depicted as an old man wearing a nightcap and carrying a bag of sand, from which he sprinkles sand over the eyes of sleeping children. The Sandman is also a popular character in literature, appearing in works such as E.T.A. Hoffmann's 1816 story 'The Sandman'.