Definition of penumbra noun from the Oxford Advanced American Dictionary

     

    penumbra

     noun
    noun
    NAmE//pəˈnʌmbrə//
     
    (technology)
     
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  1. 1an area of shadow that 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 the Oxford Advanced Learner's Dictionary entry: penumbra