penumbra plural
pe·num·bra
The plural form of penumbra is penumbras
P pDefinitions
- noun plural penumbra Astronomy. 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. Compare umbra (def 3a). the grayish marginal portion of a sunspot. Compare umbra (def 3b). 1
- noun plural penumbra a shadowy, indefinite, or marginal area. 1