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

     

    X

     noun
    noun
    BrE BrE//eks//
     
    ; NAmE NAmE//eks//
     
    (also x)(pl. Xs, X’s, x’s
    BrE BrE//ˈeksɪz//
     
    ; NAmE NAmE//ˈeksɪz//
     
    )
     
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  1. 1 [countable, uncountable] the 24th letter of the English alphabet ‘Xylophone’ begins with (an) X/‘X’.
  2. 2 [uncountable] (mathematics) used to represent a number whose value is not mentioned The equation is impossible for any value of x greater than 2.
  3. 3[uncountable] a person, a number, an influence, etc. that is not known or not named Let's suppose X knows what Y is doing.
  4. see also X chromosome, X-rated, X-ray
See the Oxford Advanced American Dictionary entry: X