Frequency: The word is one of the 700 most common words in English.
1.
If something happens once, it happens one time only.
I met Wilma once, briefly...
Since that evening I haven't once slept through the night...
Mary had only been to Manchester once before.
ADV: ADV with v
•
Once is also a pronoun.
'Have they been to visit you yet?'-'Just the once, yeah.'...
Listen to us, if only this once.
PRON: the/this PRON
2.
You use once with 'a' and words like 'day', 'week', and 'month' to indicate that something happens regularly, one time in each day, week, or month.
Lung cells die and are replaced about once a week...
We arranged a special social event once a year to which we invited our major customers.
ADV: ADV a n
3.
If something was once true, it was true at some time in the past, but is no longer true.
The culture minister once ran a theatre...
I lived there once myself, before I got married...
The house where she lives was once the village post office...
My memory isn't as good as it once was.
ADV: ADV with v, ADV with be, ADV with group/cl
4.
If someone once did something, they did it at some time in the past.
I once went camping at Lake Darling with a friend...
We once walked across London at two in the morning...
Diana had taken that path once.
ADV: ADV with v
5.
If something happens once another thing has happened, it happens immediately afterwards.
The decision had taken about 10 seconds once he'd read a market research study...
Once customers come to rely on these systems they almost never take their business elsewhere...
CONJ
6.
If something happens all at once, it happens suddenly, often when you are not expecting it to happen.
All at once there was someone knocking on the door.
= all of a sudden
PHRASE: PHR with cl
7.
If you do something at once, you do it immediately.
I have to go, I really must, at once...
Remove from the heat, add the parsley, toss and serve at once...
The audience at once greeted him warmly.
= immediately
PHRASE: PHR with v
8.
If a number of different things happen at once or all at once, they all happen at the same time.
You can't be doing two things at once...
No bank could ever pay off its creditors if they all demanded their money at once...
PHRASE: PHR after v, PHR adj/n and adj/n
9.
For once is used to emphasize that something happens on this particular occasion, especially if it has never happened before, and may never happen again.
For once, dad is not complaining...
His smile, for once, was genuine.
PHRASE: PHR with cl [emphasis]
10.
If something happens once again or once more, it happens again.
Amy picked up the hairbrush and smoothed her hair once more...
Once again an official inquiry has spoken of weak management and ill-trained workers.
PHRASE: PHR with v, PHR with cl
11.
If something happens once and for all, it happens completely or finally.
We have to resolve this matter once and for all...
If we act fast, we can once and for all prevent wild animals in Britain from suffering terrible cruelty.
PHRASE: PHR with v [emphasis]
12.
If something happens once in a while, it happens sometimes, but not very often.
Earrings need to be taken out and cleaned once in a while.
= occasionally
PHRASE: PHR with cl
13.
If you have done something once or twice, you have done it a few times, but not very often.
I popped my head round the door once or twice...
Once or twice she had caught a flash of interest in William's eyes...
PHRASE: PHR with cl, PHR with v
14.
Once upon a time is used to indicate that something happened or existed a long time ago or in an imaginary world. It is often used at the beginning of children's stories.
'Once upon a time,' he began, 'there was a man who had everything.'...
Once upon a time, asking a woman if she has a job was quite a straightforward question.
PHRASE: PHR with cl
15.
once in a blue moon: see
moon