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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.
n, pl -brae (-briː) or -bras
1. (Astronomy) a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
2. (Astronomy) astronomy the lighter and outer region of a sunspot
3. (Art Terms) painting the point or area in which light and shade blend
[C17: via New Latin from Latin paene almost + umbra shadow]
peˈnumbral, peˈnumbrous adj
n., pl. -brae (-brē), -bras.
a. the partial or imperfect shadow outside the complete shadow of an opaque body, as a planet, where the light from the source of illumination is only partly cut off.
b. the grayish marginal portion of a sunspot.
2. a shadowy, indefinite, or marginal area.
[1660–70; < New Latin, = Latin paen(e) almost + umbra shade]
pe•num′bral, pe•num′brous, adj.
1. A partial shadow between regions of complete shadow and complete illumination, especially as cast by Earth, or the moon, over another body during an eclipse.
2. The grayish outer part of a sunspot. Compare umbra.