Definition of passing noun from the Oxford Advanced American Dictionary

      

    passing

     noun
    noun
    NAmE//ˈpæsɪŋ//
     
    [uncountable]
     
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  1. 1the passing of time/the years the process of time going by
  2. 2(formal) the fact of something ending or of someone dying When the government is finally brought down, no one will mourn its passing. the passing of the old year (= on New Year's Eve) Many will mourn her passing (= her death, when you do not want to say this directly).
  3. 3the passing of something the act of making something become a law the passing of a resolution/law
  4. Idioms done or said while you are giving your attention to something else synonym casually He only mentioned it in passing and didn't give any details.
See the Oxford Advanced Learner's Dictionary entry: passing