Which is correct, goodnight or good

Which is correct, goodnight or good night?
I've seen people use both. Spell check doesn't correct goodnight.
If I understand correctly is, you can say good night like "Have a good night."
Or goodnight like "Goodnight." (like, when someone's leaving or whatever.
Are both correct? In what contexts?

ผลลัพธ์ (อังกฤษ) 2:

Which is Correct, Goodnight or good Night?
I've seen People Use Both. Spell Check does Not Correct Goodnight.
If I Understand correctly is, You Can Say good Night like "Have a good Night.".
Or like Goodnight "Goodnight.". (Like, When someone's Leaving or Whatever.
Are Both Correct? In What contexts?