a)SUDDENLYif something happens all at once, it happens suddenly when you are not expecting it 一下子,突然
All at once there was a loud banging on the door.
突然传来一记重重的敲门声。
b)together, at the same time 一起,同时
A lot of practical details needed to be attended to all at once.
许多实际上的细节问题都需要同时处理。
Examples from the Corpus
all at once• This is a distinctive and often very funnypicture, disquieting and divertingall at once.• Should we send the packagesall at once?• Employees at the plant are experiencing a-change overload. --- Changes came too fast and hit thern all at once.• Father Timothy was kind and bad all at once.• I have never seen so many injunctionsall at once.• The cold in our house made it clear all at once.• Not all at once and not so anyone could tell.• And with the slow-going afternoon the world all at once can make perfectsense.• All at once, she broke into a smile.• All at once the trailer started shaking.