Definition of umbra noun from the Oxford Advanced American Dictionary

     

    umbra

     noun
    noun
    NAmE//ˈʌmbrə//
     
    (pl. umbras or umbrae
    NAmE//ˈʌmbri//
     
    )
    (technology)
     
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  1. 1the darkest part of a shadow
  2. 2the area on the earth or the moon that is the darkest during an eclipse compare penumbra
See the Oxford Advanced Learner's Dictionary entry: umbra