Longman Dictionary of Contemporary English homepage

Date: 1200-1300
Origin: one

once

1 adverb
     
once1 S1 W1
1 on one occasion only:
I've only met her once.
Paul's been to Wexford once before.
(just) the once British English spoken:
Mrs Peterson came in to see Ruth just the once.
2

once a week/once every three months etc

one time every week etc, as a regular activity or event:
Staff meetings take place once a week.
They took separate holidays at least once every two years.
3 at some time in the past, but not now:
Sonya and Ida had once been close friends.
She and her husband had once owned a house like this.
once-great/proud etc
It was sad to see the once-great man looking so frail.
the once-mighty steel industry
4 in the past, at a time that is not stated:
I once ran 21 miles.
Marx once described religion as the 'opium of the people'.
5

at once

a) immediately or without delay:
Now, go upstairs at once and clean your room!
When I saw him I recognized him at once.
b) together, at the same time:
I can't do two things at once!
Don't all talk at once.
6

once more/once again

a) again, after happening several times before:
I looked at myself in the mirror once more.
Once again she's refusing to help.
b) used to say that a situation changes back to its previous state:
The crowds had all gone home and the street was quiet once more.
c) formal used before you repeat something that you said before:
Once again, it must be stressed that the pilot was not to blame.
7

all at once

a) if 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.
8

(every) once in a while

sometimes, although not often:
I do get a little anxious once in a while.
I saw her in the shop every once in a while.
9

never once/not once

used to emphasize that something has never happened:
I never once saw him get angry or upset.
Not once did they finish a job properly.
10

(just) for once

used to say that something unusual happens, especially when you wish it would happen more often:
Be honest for once.
Just for once, let me make my own decision.
For once Colin was speechless.
11

once and for all

a) if you deal with something once and for all, you deal with it completely and finally:
Let's settle this matter once and for all.
b) British English spoken used to emphasize your impatience when you ask or say something that you have asked or said many times before:
Once and for all, will you switch off that television!
12

once or twice

a few times:
I wrote to him once or twice, but he didn't answer.
13

(just) this once

spoken used to emphasize that this is the only time you are allowing something, asking for something etc, and it will not happen again:
Go on, lend me the car, just this once.
I'll make an exception this once.
14

once upon a time

a) spoken at a time in the past that you think was much better than now:
Once upon a time you used to be able to leave your front door unlocked.
b) a long time ago - used at the beginning of children's stories
15

once in a blue moon

informal very rarely:
It only happens like this once in a blue moon.
16

do something once too often

to repeat a bad, stupid, or dangerous action with the result that you get punished or cause trouble for yourself:
He tried that trick once too often and in the end they caught him.
17

once a ..., always a ...

spoken used to say that people stay the same and cannot change the way they behave and think:
Once a thief, always a thief.
18

once is/was enough

spoken used to say that after you have done something one time you do not need or want to do it again
19

once bitten, twice shy

used to say that people will not do something again if it has been a bad experience

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