D defs.my
Entry 3 senses Webster, 1913

Penumbra

/pĭ-nŭm'brə/ · Pe·num·bra · IPA /pəˈnʌm.bɹə/
01 n. An incomplete or partial shadow.
  1. 1.
    An incomplete or partial shadow.
  2. 2.
    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.(Astron.)
  3. 3.
    The part of a picture where the shade imperceptibly blends with the light.(Paint.)