Definition of O noun from the Oxford Advanced Learner's Dictionary

     

    O

     noun
    noun
    BrE BrE//əʊ//
     
    ; NAmE NAmE////
     
    (also o)(pl. Os, O’s, o’s
    BrE BrE//əʊz//
     
    ; NAmE NAmE//oʊz//
     
    )
     
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  1. 1 [countable, uncountable] the 15th letter of the English alphabet ‘Orange’ begins with (an) O/‘O’.
  2. 2used to mean ‘zero’ when saying telephone numbers, etc. My number is six o double three (= 6033).
  3. see also O grade, O level
See the Oxford Advanced American Dictionary entry: O