pen·um·bra /pəˈnʌmbrə/
  半影
  pe·num·bra /pəˈnəmbrə/ 名詞
  Pe·num·bra n.
  1. An incomplete or partial shadow.
  2. Astron. The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light.
  Note: ☞ The faint shade surrounding the dark central portion of a solar spot is also called the penumbra, and sometimes umbra.
  3. Paint. The part of a picture where the shade imperceptibly blends with the light.
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  penumbra
       n : a fringe region of partial shadow around an umbra
       [also: penumbrae (pl)]