goodnight
interj. A1 Beginner US //ˈɡʊdˌnaɪt// UK //ɡʊdnˈaɪt// good·night
interj. a polite way to say goodbye to someone at the end of the day or before they go to sleep.
interj. a conventional expression of farewell used in the late evening or immediately before retiring for the night.
Goodnight, see you in the morning.
She kissed her children on the forehead and whispered goodnight before turning off the light.
As the dinner party wound down and the last guests departed into the cool evening air, the host stood at the door to bid each one a warm goodnight.
From good + night.
Usage
Used exclusively as a farewell; never used as a greeting upon arrival in the evening.