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n. pl. pe·num·bras or pe·num·brae (-brē)
1. A partial shadow, as in an eclipse, between regions of complete shadow and complete illumination.
2. The diffuse 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).
[New Latin pēnumbra : Latin paene, almost + Latin umbra, shadow.]
pe·num′bral, pe·num′brous adj.
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|Adj.||1.||penumbral - of or pertaining to the region of partial shadow around an umbra|