Definition of half noun from the Oxford Advanced American Dictionary

      

    half

     noun
    noun
    NAmE//hæf//
     
    (pl. halves
    NAmE//hævz//
     
    )
     
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  1. 1 either of two equal parts into which something is or can be divided two and a half pounds (2½ lbs) One and a half hours are allowed for the exam. An hour and a half is allowed for the exam. The second half of the book is more exciting. I've divided the money in half. We'll need to reduce the weight by half. see also halve
  2. 2 either of two periods of time into which a sports game, concert, etc. is divided No goals were scored in the first half.
  3. 3 = halfback
  4. Idioms
    and a half(informal)
     
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    bigger, better, more important, etc. than usual That was a game and a half!
    go halves (with somebody)
     
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    to share the cost of something equally with someone We go halves on all the bills.
    the half of it
     
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    used in negative sentences to say that a situation is worse or more complicated than someone thinks “It sounds very difficult.” “You don't know the half of it.”
      have a good mind to do something,have half a mind to do something
       
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    1. 1used to say that you think you will do something, although you are not sure I've half a mind to come with you tomorrow.
    2. 2used to say that you disapprove of what someone has done and should do something about it, although you probably will not I've a good mind to write and tell your parents about it.
    how the other half lives
     
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    the way of life of a different social group, especially one much richer than you
    it's six of one and half a dozen of the other(saying)
     
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    used to say that there is not much real difference between two possible choices
    not do things/anything by halves
     
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    to do whatever you do completely and thoroughly You're expecting twins? Well, you never did do things by halves.
    time and a half
     
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    one and a half times the usual rate of pay We get time and a half on Sundays. see also double time
Grammarhalf / whole / quarterQuarter, half, and whole can all be nouns:Cut the apple into quarters. Two halves make a whole.Whole is also an adjective:I’ve been waiting here for a whole hour.Half is also a determiner:Half (of) the work is already finished. They spent half the time looking for a parking space. Her house is half a mile down the road.Note that you do not put a or the in front of half when it is used in this way:I waited for half an hour I waited for a half an hour.Half can also be used as an adverb:This meal is only half cooked.
See the Oxford Advanced Learner's Dictionary entry: half