Generally, the Japanese expression for saying “goodnight” is “おやすみ“(Oyasumi).

Is Oyasumi a name?

The meaning of oyasumi (and the meaning of oyasuminasai) is deceptively simple. Oyasumi means, “Good night.” Oyasumi–nasai means, “Good night,” but is a little more polite.

What is Oyasuminasai Japanese?

おやすみなさい [OYASUMINASAI] good night. In a casual way, you can say OYASUMI.