～おしまい (おわり)
～おしまい (おわり) · ～oshimai (owari) · JLPT N2 · noun
end up ~
🏁 o + shimai = polite o + the finish, from shimau: to finish, put away
Shimai is the noun form of shimau, the same verb behind ~te shimau, meaning to end up doing something. Add the polite o and you get oshimai: it's over, that's the end. Owari, from owaru (to end), means the same thing.