How to Say "Goodnight" in Japanese

おやすみなさい

oyasuminasai

goodnight in Japanese is おやすみなさい (oyasuminasai).

This phrase is used specifically when someone is actually going to sleep or when parting ways late at night.

What does it mean word for word?

Literally, おやすみなさい means "please rest."

The shortened form おやすみ is used for a casual "goodnight", whereas the full version おやすみなさい is more polite.

The phrase is a fixed expression and does not change based on the gender of the speaker.

oyasuminasai

Unlike English 'goodnight', which can be said while walking into a room as a greeting if it is late, おやすみなさい is strictly an exit phrase. Saying it upon arriving at a party would imply you intend to go straight to bed.
If you say おやすみなさい to someone who is not actually going to bed, it can sound as if you are abruptly ending the conversation or even dismissing them.
The word やすみ is the same root used for 'holiday' or 'day off' in Japanese. Wishing someone a 'goodnight' is linguistically the same as wishing them a 'rest' or a 'break' from their daily duties.

おやすみなさい。
Goodnight!
This is useful for a standard way to say おやすみなさい.
Tatoeba #426899 by qahwa, translation #1068125 by erik21889
それでは、おやすみなさい。
Sore de wa, oyasuminasai.
Well then, goodnight.
1 more sentence on Tatoeba

A couple is saying goodbye before going to sleep in their respective rooms.

結衣 Yui

明日も早いから、おやすみなさい。
Ashita mo hayai kara, oyasuminasai.
It is early tomorrow too, so goodnight.
大翔 Hiroto

うん、結衣もおやすみなさい。
Un, Yui mo oyasuminasai.
Yeah, goodnight to you too, Yui.
結衣 Yui

おやすみなさい、大翔。
Oyasuminasai, Hiroto.
Goodnight, Hiroto.
大翔 Hiroto

おやすみ。
Oyasumi.
Goodnight.

Sources

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