penumbra Meaning, Definition & Usage

  1. noun a fringe region of partial shadow around an umbra

WordNet

Pe*num"bra noun
Etymology
NL., fr. L. paene almost + umbra shade.
Definitions
  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. Sir I. Newton. ✍ 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.

Webster 1913