All at Once
WordNet
adverb
(1) Without warning
"All at once, he started shouting"
(2) All at the same time
"Let's say `Yes!' all at once"
WiktionaryText
Adverb
- Unexpectedly; without warning; all of a sudden.
- When all at once I saw a crowd, A host, of golden daffodils - William Wordsworth, Daffodils
- All at the same time; all together.
- There are too many to get in the lift all at once, so some must wait.