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Definition of millennium noun from the Oxford Advanced American Dictionary

     

    millennium

     noun
    noun
    NAmE//məˈlɛniəm//
     
    (pl. millennia
    NAmE//məˈlɛniə//
     
    , (or )millenniums)
     
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  1. 1 a period of 1,000 years, especially as calculated before or after the birth of Christ the second millennium A.D. For millennia, it was accepted that the earth was at the center of the universe.
  2. 2 the millennium the time when one period of 1,000 years ends and another begins How did you celebrate the millennium?
See the Oxford Advanced Learner's Dictionary entry: millennium