An incomplete or partial shadow.
- A partial shadow, as in an eclipse, between regions of complete shadow and complete illumination. See Synonyms at shade.
- The grayish outer part of a sunspot.
- An area in which something exists to a lesser or uncertain degree: "The First Amendment has a penumbra where privacy is protected from governmental intrusion” ( Joseph A. Califano, Jr.)
- An outlying surrounding region; a periphery: "Downtown Chicago and its penumbra also stand rejuvenated” ( John McCormick).