the end; closing; being done for
Polite noun for the end or conclusion of something; often used in the phrase おしまいにする (to finish/stop). The gloss 'being done for' refers to being ruined or finished in a negative sense.
See also: 仕舞い
That's the end of today's class.
もうおしまいだ。
It's all over now.
that's it; that's enough; that's all
Interjection used to declare that something is finished, enough, or settled; often said when stopping an activity or concluding a matter.
おしまい！もう遊びは終わりだよ。
That's it! Playtime is over.
おしまい、おしまい。その話はもうやめよう。
That's enough. Let's stop talking about that.
That's the end of class.
Let's put an end to this conversation.
If you give up here, it's all over.
I lost my wallet—I'm done for.