all at once

• (Received Pronunciation) IPA^(key): /ˌɔːl ət ˈwʌn(t)s/
• (General American) IPA^(key): /ˌɔl ət ˈwʌn(t)s/, /ˌɑl ət ˈwʌn(t)s/

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all at once (not comparable)

1. (idiomatic) Unexpectedly; without warning; all of a sudden.
   • 1815, William Wordsworth, The Daffodils:

     When all at once I saw a crowd, / A host, of golden daffodils

   • 1913, Joseph C[rosby] Lincoln, chapter IV, in Mr. Pratt’s Patients, New York, N.Y., London: D[aniel] Appleton and Company, →OCLC:

     I was on my way to the door, but all at once, through the fog in my head, I began to sight one reef that I hadn't paid any attention to afore.

2. Used other than figuratively or idiomatically: All at the same time; all together.

   There are too many to get in the lift all at once, so some must wait.