for once

WordReference Random House Learner's Dictionary of American English © 2025

once /wʌns/   adv. 

1. formerly:
   a once powerful nation.
2. a single time:
   We eat out once a week.
3. at any time;
   ever:
   If the facts once became known, we'd be in trouble.
4. by a single step, degree, or grade:
   She's my first cousin once removed.

n. [uncountable]

5. a single occasion;
   one time only:
   Once is enough.

conj. 

6. if or when at any time;
   if ever:
   Once the news is out, they'll hunt us down.
7. whenever;
   as soon as:
   Once you're finished, you can leave.

adj. 

8. former;
   one-time:
   the once and future king.

Idioms

9. Idioms all at once, suddenly:
   All at once it started to rain.
10. Idioms at once:
    • immediately;
      promptly:
      left at once.
    • at the same time;
      simultaneously:
      They all sprang up at once.
11. Idioms once (and) for all, decisively;
    finally:
    Let's settle this argument once and for all.
12. Idioms once in a while, sometimes;
    occasionally.
13. Idioms once or twice, a very few times;
    not frequently:
    I've only seen her once or twice.
14. Idioms once upon a time, (used as an opening phrase to give the setting for a fairy tale or similar story in the distant, imaginary past):
    Once upon a time there was a giant.

WordReference Random House Unabridged Dictionary of American English © 2025

once  (wuns), adv. 

1. at one time in the past;
   formerly:
   I was a farmer once; a once powerful nation.
2. a single time:
   We ate there just once. We go to a movie once a week.
3. even a single time;
   at any time;
   ever:
   If the facts once become known, it will be just too bad.
4. by a single step, degree, or grade:
   a cousin once removed.
5. Idioms once and again, repeatedly:
   He has been told once and again not to slam the door.
6. Idioms once and for all, decisively;
   finally:
   Let's settle this problem once and for all.
   Also, once for all. 
7. Idioms once in a while, at intervals;
   occasionally:
   She stops in to see us once in a while.
8. Idioms once or twice, a very few times;
   infrequently:
   I've seen her in the elevator once or twice.
9. Idioms once upon a time, at some unspecified past time, esp. a long time ago:
   Once upon a time, in a faraway land, there lived a prince and princess.

adj. 

10. former;
    having at one time been:
    the once and future king.

conj. 

11. if or when at any time;
    if ever.
12. whenever;
    as soon as:
    Once you're finished, you can leave.

n. 

13. a single occasion;
    one time only:
    Once is enough.
14. Idioms all at once:
    • simultaneously:
      The children were running, screaming, and throwing things all at once.
    • suddenly:
      All at once the rain came down.
15. Idioms at once:
    • at the same time;
      simultaneously:
      Don't all speak at once.
    • immediately;
      promptly:
      Tell him to come at once!

• bef. 1150; Middle English ones, Old English ānes, origin, originally genitive of ān one; replacing Middle English enes, Old English ǣnes once, equivalent. to ǣne once (origin, originally instrumental of ān) + -es adverb, adverbial suffix; see -s¹

Collins Concise English Dictionary © HarperCollins Publishers::

once / wʌns/ adverb

1. one time; on one occasion or in one case
2. at some past time; formerly: I could speak French once
3. by one step or degree (of relationship): a cousin once removed
4. (in conditional clauses, negatives, etc) ever; at all: if you once forget it
5. multiplied by one
6. once and away ⇒ conclusively
7. occasionally
8. once and for all ⇒ conclusively; for the last time
9. once in a while ⇒ occasionally; now and then
10. once or twice, once and again ⇒ a few times
11. once upon a time ⇒ used to begin fairy tales and children's stories

conjunction

1. (subordinating) as soon as; if ever or whenever

noun

1. one occasion or case: you may do it, this once
2. all at once ⇒ suddenly or without warning
3. simultaneously
4. at once ⇒ immediately
5. simultaneously
6. for once ⇒ this time, if (or but) at no other time

Etymology: 12th Century ones, ānes, adverbial genitive of on, ān one