Meaning of penumbra
Pronunciation: (pi-num'bru), [key]
— pl. -brae -bras.
- 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. Cf.umbra(def. 3a).
- the grayish marginal portion of a sunspot. Cf.umbra(def. 3b).
- a shadowy, indefinite, or marginal area.
- penumbra (Thesaurus)