Definition of: penumbra

(pi·num′brə) noun plural ·brae (-brē) or ·bras
1. A margin of a shadow within which the rays of light from an illuminating body are partly but not wholly intercepted.
2. Astron. a The partial shadow between the umbra, or region of total eclipse, and the region of unobstructed light. b The dark fringe around the central part of a sunspot.
3. In painting, the blending point, or line between light and shade. [<NL <L paene almost + umbra a shadow]
—pe·num′bral, pe·num′brous (-brəs) adjective