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

     

    penumbra

     noun
    noun
    BrE BrE//pəˈnʌmbrə//
     
    ; NAmE NAmE//pəˈnʌmbrə//
     
    (specialist) The sun and the moon
     
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  1. 1an area of shadow which is between fully dark and fully light
  2. 2(astronomy) the shadow made by the earth or the moon during a partial eclipse compare umbra See related entries: The sun and the moon
  3. Word Origin mid 17th cent.: modern Latin, from Latin paene ‘almost’ + umbra ‘shadow’.
See the Oxford Advanced American Dictionary entry: penumbra