I. one 1 S1 W1 /wʌn/ BrE AmE number
1 . the number 1:
They had one daughter.
one hundred and twenty-one pounds
Come back at one (=one o'clock) .
Katie’s almost one (=one year old) .
2 . one or two a small number of people or things SYN a few :
There are one or two things to sort out before I leave.
one or two of
One or two of us knew him quite well.
3 . in ones and twos British English alone or in pairs, rather than in large numbers or groups:
Guests arrived in ones and twos.
II. one 2 S1 W1 BrE AmE pronoun ( plural ones )
1 . used to mean someone or something of a type that has already been mentioned or is known about:
‘Have you got a camera?’ ‘No.’ ‘You should buy one (=buy a camera) .'
The train was crowded so we decided to catch a later one (=catch a later train) .
the one(s) (that/who/which)
The only jokes I tell are the ones that I hear from you.
this one/that one/these ones/those ones
I like all the pictures except this one.
2 . used to refer to a member of a group or pair of people or things:
The children seemed upset. One was crying.
She has two daughters. One is a primary school teacher, the other is a musician.
One of the girls I work with is getting married.
This is one of my favourite books.
One of is followed by a plural noun but a singular verb:
One of the windows was open.
3 . the one(s) who/that the person or people who:
I was the one who had been attacked, not Richard.
The only ones who will benefit are the shareholders.
4 . one by one used when one person or thing in a group does something, then the next, then the next, especially in a regular way:
One by one each soldier approached the coffin and gave a final salute.
5 . one after another/one after the other if events happen one after the other, they happen without much time between them:
One after another, tropical storms battered the Pacific coastline.
6 . (all) in one if someone or something is many different things all in one, they are all those things:
It’s a TV, radio, and VCR all in one.
7 . formal used to mean people in general, including yourself:
One can never be too careful.
Great pictures make one think.
In everyday English, people usually use you rather than one :
You can never be too careful.
8 . I, for one, ... used to emphasize that you believe something, will do something etc and hope others will do the same:
I, for one, am proud of the team’s effort.
9 . ... for one used to give an example of someone or something:
There were several other people absent that afternoon, weren’t there? Mr Ashton for one.
10 . be one up (on somebody)/get one up on somebody to have or get an advantage over someone ⇨ ↑ one-upmanship
11 . put one over on somebody informal to trick someone:
No one’s going to put one over on me!
12 . be at one with somebody/something
a) to feel very calm or relaxed in the situation or environment you are in:
She felt as she always did in these mountains: peaceful, without care, at one with nature.
b) formal to agree with someone about something:
He was at one with Wheatley on the need to abandon free trade.
13 . informal used in particular phrases to mean ‘an alcoholic drink’:
How about a quick one at the pub?
have had one too many (=have drunk too much alcohol)
(have) one for the road (=have one last alcoholic drink before you leave a place)
14 . the one about ... spoken a joke or humorous story:
Have you heard the one about the chicken who tried to cross the road?
15 . as one written if many people do something as one, they all do it at the same time:
The whole team stood up as one.
16 . a difficult/hard/good etc one a particular kind of problem, question, story etc:
‘What do you attribute your long life to?’ ‘Oh that’s a difficult one’.
17 . one and the same the same person or thing:
Muhammad Ali and Cassius Clay are one and the same.
18 . not/never be one to do something informal to never do a particular thing, because it is not part of your character to do it:
Tom is not one to show his emotions.
19 . not/never be (a great) one for (doing) something informal to not enjoy a particular activity, subject etc:
I’ve never been a great one for watersports.
20 . one of us spoken used to say that someone belongs to the same group as you, or has the same ideas, beliefs etc:
You can talk in front of Terry – he’s one of us.
21 . one and all old-fashioned or formal everyone:
Apologies to one and all.
22 . got it in one! British English spoken used to say that someone has correctly guessed or understood something immediately:
‘You’re not painting the house again are you?’ ‘Got it in one!’
23 . little/young ones spoken used by some people to mean ‘children’, especially young children:
She’s got four little ones.
24 . you are/he is a one British English old-fashioned used to say that someone’s behaviour is amusing, strange, or surprising:
You are a one!
⇨ ↑ one-to-one
III. one 3 S1 W1 BrE AmE determiner
[ Language: Old English ; Origin: an ]
1 . used to emphasize a particular person or thing:
One person I find very difficult is Bob.
If there’s one thing I can’t stand, it’s people who bite their nails.
2 . one day/morning/year etc
a) on a particular day, morning etc in the past:
One morning I was sitting at my desk when a policeman knocked at my door.
b) used to talk about a day, morning etc in the future which is not yet exactly known or decided:
We should go out for a drink one evening.
One day she hopes to move to the South Coast.
3 . used to talk about a particular person or thing in comparison with other similar people or things:
Why does my card work in one cash machine and not in another?
4 . It’s one thing to ... it’s (quite) another to used to say that the second thing mentioned is very different from the first, and is often much more difficult to do:
It’s one thing to say we have a goal; it’s another to actually act on it.
5 . for one thing used to introduce a reason for what you have just said:
He couldn’t bring himself to say what he thought. For one thing, she seldom stopped to listen. For another, he doubted that he could make himself clear.
6 . be one crazy woman/be one interesting job etc especially American English spoken to be a very crazy woman, be a very interesting job etc:
You’re one lucky guy.
7 . formal used before the name of someone you do not know or have not heard of before SYN a certain :
He was accused of stealing a horse from one Peter Wright.
IV. one 4 BrE AmE adjective [only before noun]
1 . only:
Her one concern was to get to the door without being seen.
Claire is the one person I can trust.
2 . one and only
a) used to emphasize that someone is very famous:
the one and only Frank Sinatra
b) used to emphasize that something is the only one of its kind:
I even tried my one and only French joke on them.
V. one 5 BrE AmE noun [countable usually plural] American English
a piece of paper money worth one dollar:
I don’t have any ones.