one

I. one¹ 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.

Oxford Advanced Learner's Dictionary

one

one [one ones] number, determiner, pronoun [wʌn] [wʌn]

number, determiner
1. the number 1
• Do you want one or two?
• There's only room for one person.
• One more, please!
• a one-bedroomed apartment

• I'll see you at one (= one o'clock).

2. used in formal language or for emphasis before hundred, thousand, etc, or before a unit of measurement
• It cost one hundred and fifty pounds.

• He lost by less than one second.

3. used for emphasis to mean ‘a single’ or ‘just one’

• There's only one thing we can do.

4. a person or thing, especially when they are part of a group
• One of my friends lives in Brighton.

• One place I'd really like to visit is Bali.

5. used for emphasis to mean ‘the only one’ or ‘the most important one’
• He's the one person I can trust.
• Her one concern was for the health of her baby.

• It's the one thing I can't stand about him.

6. used when you are talking about a time in the past or the future, without actually saying which one
• I saw her one afternoon last week.

• One day (= at some time in the future) you'll understand.

7. the same

• They all went off in one direction.

8. (informal, especially NAmE) used for emphasis instead of a or an
• That was one hell of a game!

• She's one snappy dresser.

9. used with a person's name to show that the speaker does not know the person
Syn: certain
• He worked as an assistant to one Mr Ming.
more at all in one at all _pron., be in a minority of one at minority, back to square one at square _n.
Word Origin:
Old English ān, of Germanic origin; related to Dutch een and German ein, from an Indo-European root shared by Latin unus. The initial w sound developed before the 15th cent. and was occasionally represented in the spelling; it was not accepted into standard English until the late 17th cent.
Grammar Point:
one / ones
One/ones is used to avoid repeating a countable noun, but there are some times when you should not use it, especially in formal speech or writing:
After a possessive (my, your, Mary’s, etc.), some, any, both or a number, unless it is used with an adjective: ▪ ‘Did you get any postcards?’ ‘Yes, I bought four nice ones.’ ◊ I bought four ones.
It can be left out after superlatives, this, that, these, those, either, neither, another, which, etc: ▪ ‘Here are the designs. Which (one) do you prefer?’ ‘I think that (one) looks the most original.’
These ones and those ones are not used in NAmE, and are unusual in BrE: ▪ Do you prefer these designs or those?
It is never used to replace uncountable nouns and is unusual with abstract countable nouns: ▪ The Scottish legal system is not the same as the English system, is better than ▪ …as the English one.

Idioms: as one ▪ at one ▪ for one ▪ get one over somebody ▪ get something in one ▪ go one better ▪ in one ▪ one after the other ▪ one and all ▪ one and only ▪ one and the same ▪ one by one ▪ one for something ▪ one or two ▪ one up ▪ when you've seen/heard one/you've seen/heard them all

Cambridge Advanced Learner's Dictionary

Cambridge Advanced Learner's Dictionary - 4th Edition

one / wʌn / number , determiner (NUMBER)

A1 the number 1:

You've got three bags and I've only got one.

She'll be one year old tomorrow.

Collins Advanced Learner’s English Dictionary

one

[wʌ̱n]
♦
ones
1) NUM One is the number 1.
  They had three sons and one daughter.
  ...one thousand years ago...
  Scotland beat England one-nil at Wembley.
  ...one of the children killed in the crash.
2) ADJ: det ADJ (emphasis) If you say that someone or something is the one person or thing of a particular kind, you are emphasizing that they are the only person or thing of that kind.
  They had alienated the one man who knew the business...
  His one regret is that he has never learned a language.
  Syn:
  only
3) DET: DET sing-n (emphasis) One can be used instead of `a' to emphasize the following noun.
  There is one thing I would like to know - What is it about Tim that you find so irresistible?...
  One person I hate is Russ.
4) DET: DET adj sing-n (emphasis) You can use one instead of `a' to emphasize the following adjective or expression. [INFORMAL]
  If we ever get married we'll have one terrific wedding...
  It's like one enormous street carnival here.
5) DET: DET n-proper You can use one in front of someone's name to indicate that you have not met them or heard of them before. [FORMAL]
  It seems that the fifth man is one John Cairncross.
  Syn:
  a certain
6) DET: DET sing-n You can use one to refer to the first of two or more things that you are comparing.
  Prices vary from one shop to another...
  The road hugs the coast for hundreds of miles, the South China Sea on one side, jungle on the other.
ADJ: det ADJ
One is also an adjective. We ask why peace should have an apparent chance in the one territory and not the other.
PRON
One is also a pronoun. The twins were dressed differently and one was thinner than the other.
7) PRON You can use one or ones instead of a noun when it is clear what type of thing or person you are referring to and you are describing them or giving more information about them.
  They are selling their house to move to a smaller one...
  We test each one to see that it flies well.
8) PRON You use ones to refer to people in general.
  We are the only ones who know.
9) PRON: PRON of n, PRON that You can use one instead of a noun group when you have just mentioned something and you want to describe it or give more information about it.
  His response is one of anger and frustration...
  The issue of land reform was one that dominated Hungary's parliamentary elections.
10) DET: DET sing-n You can use one when you have been talking or writing about a group of people or things and you want to say something about a particular member of the group.
  `A college degree isn't enough', said one honors student.
PRON
One is also a pronoun. Some of them couldn't eat a thing. One couldn't even drink.
11) QUANT: QUANT of adj-superl You use one in expressions such as `one of the biggest airports' or `one of the most experienced players' to indicate that something or someone is bigger or more experienced than most other things or people of the same kind.
  Subaru is one of the smallest Japanese car makers.
12) DET: DET sing-n You can use one when referring to a time in the past or in the future. For example, if you say that you did something one day, you mean that you did it on a day in the past.
one day → see day
  How would you like to have dinner one night, just you and me?...
  Then one evening Harry phoned, asking me to come to their flat as soon as possible.
13) PRON: with supp You can use one to refer to a question, joke, remark, or subject of discussion.
  This is a tricky one to answer...
  Have you heard the one about the Irishman, the Englishman and the American?...
  I told him I'd have to think about that one.
14) PRON You can use one to refer to an alcoholic drink. [INFORMAL]
  Other members of the committee drifted in for a quick one before closing time.
15) PRON You use one to make statements about people in general which also apply to themselves. One can be used as the subject or object of a sentence. [FORMAL]
  If one looks at the longer run, a lot of positive things are happening...
  Where does one go from there?...
  Shares and bonds can bring one quite a considerable additional income.
16) PHRASE: PHR after v If a group of people does something as one, all the people do the same thing at the same time or in the same way. [WRITTEN]
  The 40,000 crowd rose as one.
17) PHRASE: oft with brd-neg, v-link PHR n/-ing If you say that someone is one for or is a one for something, you mean that they like or approve of it or enjoy doing it.
  I'm not one for political discussions...
  She was a real one for flirting with the boys.
18) PHRASE: PHR before v (emphasis) You can use for one to emphasize that a particular person is definitely reacting or behaving in a particular way, even if other people are not.
  I, for one, hope you don't get the job.
19) PHRASE: usu PHR pl-n (emphasis) You can use expressions such as a hundred and one, a thousand and one, and a million and one to emphasize that you are talking about a large number of things or people.
  There are a hundred and one ways in which you can raise money.
20) PHRASE: pl-n PHR, PHR after v You can use in one to indicate that something is a single unit, but is made up of several different parts or has several different functions.
  ...a love story and an adventure all in one...
  This cream moisturises and repairs in one.
21) PHRASE: PHR with cl You can use in ones and twos to indicate that people do things or something happens gradually and in small groups.
  They lose interest and start drifting away in ones and twos.
22) PHRASE: PHR with cl You use one after the other or one after another to say that actions or events happen with very little time between them.
  My three guitars broke one after the other...
  One after another, people described how hard it is for them to get medical care.
23) PHRASE: PHR n-proper The one and only can be used in front of the name of an actor, singer, or other famous person when they are being introduced on a show.
  ...one of the greatest ever rock performers, the one and only Tina Turner.
24) PHRASE: PHR with cl You can use one by one to indicate that people do things or that things happen in sequence, not all at the same time.
  We went into the room one by one...
  One by one the houses burst into flames.
25) PHRASE: usu PHR of pl-n You use one or other to refer to one or more things or people in a group, when it does not matter which particular one or ones are thought of or chosen.
  One or other of the two women was wrong.
26) PHRASE: oft PHR pl-n, PHR of pl-n One or two means a few.
  We may make one or two changes...
  I've also sold one or two to an American publisher...
  I asked one or two of the stallholders about it.
  Syn:
  a few
27) PHRASE: PHR to-inf, usu v-link PHR If you say that someone is not one to do something, you think that it is very unlikely that they would do it because it is not their normal behaviour.
  I'm not one to waste time on just anyone.
28) PHRASE: PHR n, usu v-link PHR, PHR after v If you try to get one up on someone, you try to gain an advantage over them.
  ...the competitive kind who will see this as the opportunity to be one up on you.

Merriam-Webster's Advanced Learner's Dictionary

¹one /ˈwʌn/ noun, pl ones
1 [count] : the number 1
• one, two, three, four, …
2 [count] US : a one-dollar bill
• I don't have any ones. Can you break a five?
3 [noncount] : one o'clock
• I'll be there at one.
4 [count] : the first in a set or series
• On day one of his diet, he cut out sweets.
• She wears a size one.
as one formal
1 : at the same time : all together
• They rose as one and cheered her.
2 : in agreement with each other
• We are as one on this issue.
at one with
1 : in a peaceful state as a part of something else
• I feel at one with nature. [=I feel very closely connected to nature]
2 formal : in a state of agreement with another person
• I am at one with you on this issue.
for one : as an example
• I, for one, disagree. [=I disagree]
• There were many spelling mistakes in the essay. “There” for “their,” for one.
in one : combined in a single thing
• a dictionary and thesaurus (all) in one
• a DVD and VCR player in one
the odd one out
- see ¹odd