good night
From Longman Dictionary of Contemporary Englishgood nightgood ˈnight ●●● S3 GOODBYESLEEPused to say goodbye when you are leaving someone or they are leaving at night, or before going to sleep → good evening Good night. Sleep well.RegisterIn informal everyday English, people often just say Night or, especially to children, Night night:Night night, darling. See you in the morning.