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).