all at once,
    1. simultaneously: The children were running, screaming, and throwing things all at once.
    2. suddenly: All at once the rain came down.
    at once,
    1. at the same time; simultaneously: Don't all speak at once.
    2. immediately; promptly: Tell him to come at once!
    once and again, repeatedly: He has been told once and again not to slam the door.
    once and for all, decisively; finally: Let's settle this problem once and for all.Also once for all.
    once in a while, at intervals; occasionally: She stops in to see us once in a while.
    once or twice, a very few times; infrequently: I've seen her in the elevator once or twice.
    once upon a time, at some unspecified past time, especially a long time ago: Once upon a time, in a faraway land, there lived a prince and princess.

Origin of once

before 1150; Middle English ones, Old English ānes, orig. genitive of ān one; replacing Middle English enes, Old English ǣnes once, equivalent to ǣne once (orig. instrumental of ān) + -es adv. suffix; see -s1 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for all at once



one time; on one occasion or in one case
at some past time; formerlyI could speak French once
by one step or degree (of relationship)a cousin once removed
(in conditional clauses, negatives, etc) ever; at allif you once forget it
multiplied by one
once and away
  1. conclusively
  2. occasionally
once and for all conclusively; for the last time
once in a while occasionally; now and then
once or twice or once and again a few times
once upon a time used to begin fairy tales and children's stories


(subordinating) as soon as; if ever or wheneveronce you begin, you'll enjoy it


one occasion or caseyou may do it, this once
all at once
  1. suddenly or without warning
  2. simultaneously
at once
  1. immediately
  2. simultaneously
for once this time, if (or but) at no other time

Word Origin for once

C12 ones, ānes, adverbial genitive of on, ān one
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for all at once



c.1200, anes, from ane "one" (see one ) + adverbial genitive. Replaced Old English æne. Spelling changed as pronunciation shifted from two syllables to one after c.1300. Pronunciation change to "wuns" parallels that of one. As an emphatic, meaning "once and for all," it is attested from c.1300, but this now is regarded as a Pennsylvania German dialect formation. Meaning "in a past time" (but not necessarily just one time) is from mid-13c.

Once upon a time as the beginning of a story is recorded from 1590s. At once originally (early 13c.) meant "simultaneously," later "in one company" (c.1300), and preserved the sense of "one" in the word; the phrase typically appeared as one word, atones; the modern meaning "immediately" is attested from 1530s.

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with all at once

all at once


All at the same time, as in We can't get inside all at once, so please wait your turn. [Late 1300s]


Suddenly, unexpectedly, as in All at once the sky darkened. For a synonym, see all of a sudden.


In addition to the idioms beginning with once

  • once and for all
  • once bitten, twice shy
  • once in a blue moon
  • once in a lifetime
  • once in a while
  • once over lightly
  • once upon a time

also see:

  • all at once
  • at once
  • every now and then (once in a while)
  • give someone the once-over
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.