Meaning of penumbra

pe•num•bra

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