| an expression of farewell used in parting at nighttime or when going to sleep. |
[good-nahyt] 
| a farewell or leave-taking: He said his good-nights before leaving the party. |
good night
Expression of farewell used when parting at night or when going to sleep, as in He stood at the door, saying good night to each of the departing guests, or Mother came to tuck the children in and kiss them good night. [late 1300s]
Exclamation of surprise or irritation, as in Good night, Joe!
You can't mean what you said, or Good night, Anneit's time you learned how to throw a ball. [Late 1800s]