Definition of one number from the Oxford Advanced Learner's Dictionary

      

    one

     number,determiner
    number, determiner
    BrE BrE//wʌn//
     
    ; NAmE NAmE//wʌn//
     
     
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  1. 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. 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. 3  used for emphasis to mean ‘a single’ or ‘just one’ There's only one thing we can do.
  4. 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. 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. 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. 7  the same They all went off in one direction.
  8. 8(informal, especially North American English) used for emphasis instead of a or an That was one hell of a game! She's one snappy dresser.
  9. 9used with a person’s name to show that the speaker does not know the person synonym certain (4) He worked as an assistant to one Mr Ming.
  10. 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.Idioms having two or more uses, functions, etc. It's a corkscrew and bottle-opener all in one. (formal) in agreement; all together We spoke as one on this matter.
    (be) at one (with somebody/something)
     
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    (formal) to feel that you completely agree with somebody/something, or that you are part of something a place where you can feel at one with nature
    a return to the situation you were in at the beginning of a project, task, etc., because you have made no real progress If this suggestion isn't accepted, we'll be back to square one.
    be in a minority of one
     
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    (often humorous) to be the only person to have a particular opinion or to vote a particular way
    used to emphasize that a particular person does something and that you believe other people do too I, for one, would prefer to postpone the meeting. to understand or guess something immediately ‘Oh, so she’s his sister!’ ‘Got it in one!’
    get one over (on) somebody/something
     
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    (informal) to get an advantage over somebody/something I'm not going to let them get one over on me!
    go one better (than somebody/something)
     
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    to do something better than somebody else or than you have done before synonym outdo She did well this year and next year she hopes to go one better.
    used to say that somebody/something has different roles, contains different things or is used for different purposes She's a mother and company director in one. It's a public relations office, a press office and a private office all in one. see also all-in-one
    one after another/the other
     
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    first one person or thing, and then another, and then another, up to any number or amount The bills kept coming in, one after another.
    (old-fashioned, informal) everyone Happy New Year to one and all! used to emphasize that somebody is famous Here he is, the one and only Van Morrison! used for emphasis to mean ‘the same’ I never realized Ruth Rendell and Barbara Vine were one and the same (= the same person using two different names).  separately and in order I went through the items on the list one by one.  a few We've had one or two problems—nothing serious. having an advantage over somebody
    when you’ve seen, heard, etc. one, you’ve seen, heard, etc. them all
     
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    (saying) used to say that all types of the things mentioned are very similar I don't like science fiction novels much. When you've read one, you've read them all.
See the Oxford Advanced American Dictionary entry: one