penumbra

(pĭ-nŭmˈbrə)

1. A partial shadow, as in an eclipse, between regions of complete shadow and complete illumination. See Synonyms at shade.
2. The grayish outer part of a sunspot.
3. 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.)
4. An outlying surrounding region; a periphery: “Downtown Chicago and its penumbra also stand rejuvenated” (John McCormick).

Related Forms:

• pe·numˈbral, pe·numˈbrous adjective