Use this only when you are going to go to sleep. Not when greeting someone at night, use こんばんは, konbanwa, instead.
What exactly does the 'nasai (なさい)' stand for? I understood it is polite, but why, where does it come from?
It's actually a specific way of conjugating verbs which makes them polite commands. The -なさい conjugation is often used on other verbs by parents instructing their children, or teachers when controlling their students.
As others have pointed out, 休む（やすむ）means "to rest", and by using this conjugation, the speaker is instructing the listener to get some rest. The phrase おやすみなさい no longer carries such a direct meaning, i.e. it's just a greeting now instead of being a command, but that's where it comes from.
Wait おやすみなさい means goonight as a greeting!? Like you would say when passing by someone at 7 pm? I always tought it was more like "goodnight son" kisses his forehead
No, it is when saying goodnight to someone as you leave or they are heading to bed
As @SteveHaigh1 said, おやすみない is typically a closing greeting, rather than an opening greeting. (But it's a "greeting" nonetheless.)
definitely one word in the context of oyasumi - if you were to say "tonight was a good night" then it would be two words.
I feel like it's important to clarify this means "Night" in the sense of a farewell, not "night" in the sense of after dark. Confused me for a bit.
So is saying "やすみ" kind of like saying "Night" like a shortened version of good night.
No, the shortened version of "good night" would be おやすみ. Without the お, it becomes the noun 休み meaning "holiday/break/rest", not a greeting.
Just a little lesson in English here: the correct translation for おやすみなさい is “goodnight”, not “good night”. When the space is present between “good” and “night”, “good” becomes an adjective that describes “night”. おやすみなさい is a phrase that is meant to be used when wishing someone a good night (the phrase is used as a farewell), so the correct translation of おやすみなさい is “goodnight”. The translation of “good night” is 良い夜 「よいよる」where 良い「よい」is an adjective (meaning “good”) and it is being used to describe the noun 夜「よる」(meaning “night”).
aw man, people are giving you downvotes but I really love seeing this here. Punpun is exactly how I know what おやすみ means, and in fact my learning goal is to one day be able to read it in the original Japanese.
What is the connection between good night and I am sorry? Sumimasen always get me confused in this question
I don't think there is a connection. Japanese only has so many syllables, and there are only so many ways to put them together. Occasionally, short sequences like "すみ" will pop up in different places.
Good evening is used as a greeting. Good night is used as a farewell. In particular, the おやすみ for good night means "go get some rest" or "sleep well."
Time of day.
Also, there are different ways of saying "good night" depending on whether you are merely taking your leave, or if one of you is literally about to go to bed.
Oyasumi is translated as "a break" while i recall that "nasai" is like a command, like "Have a break" Is that how it can be literally translated?
More to the point, こんばんは is for saying "hello" and "goodbye" during the evening hours and おやすみなさい is for when someone is actually going to bed. This has been discussed many times on this page already.
You're confusing sumimasen すみません
with suminasai すみなさい
These are two very different words despite some similarities.
That's a good question. I don't have a very satisfying answer, but you just have to treat greetings a little differently from most other words.
The phrase おはよう, also written お早う, comes from old Japanese. The original meaning is something along the lines of "how early you are".
It is never a greeting. It is only used when either you or the person you're talking to intends to go to bed to sleep.