good night
/ˌɡʊd ˈnaɪt/
/ˌɡʊd ˈnaɪt/
Etymology
Old EnglishEnglish
Formed from "good" plus "night", following the same pattern as "good morning" and "good day". Such parting and greeting phrases were originally short for fuller wishes like "may you have a good night", and over time the longer wish was dropped, leaving the fixed two-word formula used today.