Frequency: The word is one of the 700 most common words in English.
1.
If something happens ~, it happens one time only.
I met Wilma ~, briefly...
Since that evening I haven’t ~ slept through the night...
Mary had only been to Manchester ~ before.
ADV: ADV with v
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Once is also a pronoun.
‘Have they been to visit you yet?’—‘Just the ~, yeah.’...
Listen to us, if only this ~.
PRON: the/this PRON
2.
You use ~ 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 ~ a week...
We arranged a special social event ~ a year to which we invited our major customers.
ADV: ADV a n
3.
If something was ~ true, it was true at some time in the past, but is no longer true.
The culture minister ~ ran a theatre...
I lived there ~ myself, before I got married...
The house where she lives was ~ the village post office...
My memory isn’t as good as it ~ was.
ADV: ADV with v, ADV with be , ADV with group/cl
4.
If someone ~ did something, they did it at some time in the past.
I ~ went camping at Lake Darling with a friend...
We ~ walked across London at two in the morning...
Diana had taken that path ~.
ADV: ADV with v
5.
If something happens ~ another thing has happened, it happens immediately afterwards.
The decision had taken about 10 seconds ~ 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 ~, it happens suddenly, often when you are not expecting it to happen.
All at ~ there was someone knocking on the door.
= all of a sudden
PHRASE: PHR with cl
7.
If you do something at ~, you do it immediately.
I have to go, I really must, at ~...
Remove from the heat, add the parsley, toss and serve at ~...
The audience at ~ greeted him warmly.
= immediately
PHRASE: PHR with v
8.
If a number of different things happen at ~ or all at ~, they all happen at the same time.
You can’t be doing two things at ~...
No bank could ever pay off its creditors if they all demanded their money at ~...
PHRASE: PHR after v, PHR adj/n and adj/n
9.
For ~ is used to emphasize that something happens on this particular occasion, especially if it has never happened before, and may never happen again.
For ~, dad is not complaining...
His smile, for ~, was genuine.
PHRASE: PHR with cl emphasis
10.
If something happens ~ again or ~ more, it happens again.
Amy picked up the hairbrush and smoothed her hair ~ 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 ~ and for all, it happens completely or finally.
We have to resolve this matter ~ and for all...
If we act fast, we can ~ and for all prevent wild animals in Britain from suffering terrible cruelty.
PHRASE: PHR with v emphasis
12.
If something happens ~ in a while, it happens sometimes, but not very often.
Earrings need to be taken out and cleaned ~ in a while.
= occasionally
PHRASE: PHR with cl
13.
If you have done something ~ or twice, you have done it a few times, but not very often.
I popped my head round the door ~ 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.
~ in a blue moon: see moon