all at once

without warning; suddenly

突然

all at once the noise stopped.

突然，吵闹声停止了。

all at the same time

同时

a lot of beans are ready all at once.

同时很多豆子准备好了。

for once (或this once)

on this occasion only, as an exception

就（这）一次；破例一回

I hope you'll forgive me this once.

我希望你就原谅我这一次。

once a ——, always a ——

(proverb)a person cannot change their fundamental nature

(谚)一次…始终…

once a whinger, always a whinger.

曾经是把短刀，始终是把短刀。

once again (或more)

one more time

又一次，再一次

once and for all (或once for all)

now and for the last time; finally

一劳永逸；彻底地

once and future

denoting someone or something that is eternal, enduring, or constant

永久的；持久的；持续的

side two contains four once and future hit singles.

第二面有四首持续走红的单曲。

once bitten, twice shy

side two contains four once and future hit singles.

第二面有四首持续走红的单曲。

once (或every once) in a while

from time to time; occasionally

偶然；间或

once or twice

a few times

一两次

once upon a time

at some time in the past (used as a conventional opening of a story)

从前（用于故事的开头）

at once

All at one time; simultaneously

立刻；同时

Everything happened at once. The view of the skyline is at once awesome, grand, and disappointing.

所有的事都一起发生了。天边立刻呈现出令人敬畏的、壮丽的和令人沮丧的景色

Immediately; instantly

立即；马上

Leave the room at once.

马上离开这个房间