The lights went out all at once.
all at once
idiomUnexpectedly; without warning; all of a sudden.
The rain started falling all at once, so we ran inside to stay dry.
The silence of the library was broken all at once when the heavy wooden door slammed shut.
- 01
for this once
On this particular occasion, to make an exception
- 02
once again
Again, once more, one more time.
- 03
once and for all
Conclusively, finally, permanently.
- 04
once in a blue moon
Very rarely; very infrequently.
- 05
once in a while
Occasionally; sometimes.
- 06
once or twice
A small, indefinite number of times.