Dictionary  pe•num•braPronunciation: (pi-num'bru), [key] —n., —pl. -braePronunciation: (-brē), [key] -bras. 1. Astron. 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. Cf. umbra (def. 3a). b. the grayish marginal portion of a sunspot. Cf. umbra (def. 3b). 2. a shadowy, indefinite, or marginal area. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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