From Longman Dictionary of Contemporary Englishall at onceall at oncea) SUDDENLYif something happens all at once, it happens suddenly when you are not expecting it All at once there was a loud banging on the door. b) together, at the same time A lot of practical details needed to be attended to all at once. → once
Examples from the Corpus
all at once• This is a distinctive and often very funny picture, disquieting and diverting all at once.• Should we send the packages all 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 injunctions all 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 perfect sense.• All at once, she broke into a smile.• All at once the trailer started shaking. 