from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A partial shadow, as in an eclipse, between regions of complete shadow and complete illumination.
  • noun The diffuse outer part of a sunspot.
  • noun An area in which something exists to a lesser or uncertain degree.
  • noun An outlying surrounding region; a periphery.

from The Century Dictionary.

  • noun A surrounding fringe or border, as in the distribution of metamorphic effects produced by an igneous mass.
  • noun The partial shadow between the full light and the total shadow caused by an opaque body intercepting a part of the light from a luminous body.
  • noun The gray fringing border which surrounds the dark umbra or nucleus of a sun-spot.
  • noun In painting, the boundary of shade and light, where the one blends with the other, the gradation being almost imperceptible.

from the GNU version of the Collaborative International Dictionary of English.

  • noun An incomplete or partial shadow.
  • noun (Astron.) The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light.
  • noun (Paint.) The part of a picture where the shade imperceptibly blends with the light.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun A partially shaded area around the edges of a shadow, especially an eclipse.
  • noun astronomy A region around the edge of a sunspot, darker than the sun's surface but lighter than the middle of the sunspot.
  • noun figuratively An area of uncertainly or intermediacy between two mutually exclusive states or categories.
  • noun figuratively An area that lies on the edge of something; a fringe.
  • noun Something related to, connected to, and implied by, the existence of something else that is necessary for the second thing to be full and complete in its essential aspects.
  • noun medicine (in "ischaemic penumbra", after a stroke) A region of the brain that has lost only some of its blood supply, and retains structural integrity but has lost function.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun a fringe region of partial shadow around an umbra


from The American Heritage® Dictionary of the English Language, 4th Edition

[New Latin pēnumbra : Latin paene, almost + Latin umbra, shadow.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From New Latin penumbra, from Latin paene ("almost") + umbra ("shadow").


The word penumbra has been adopted by d6.

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  • Almost shadow.

    April 30, 2009

  • *waits for the inevitable taking of penumbrage*

    April 30, 2009

  • You know us well. :-)

    May 2, 2009

  • "n. A surrounding fringe or border, as in the distribution of metamorphic effects produced by an igneous mass." --CD&C

    March 14, 2012

  • From p. 10 of Patrick Leigh Fermor's "A Time to Keep Silence":

    This hanging pulpit framed the head and shoulders of a monk, reading from a desk by the light of a lamp which hollowed a glowing alcove out of the penumbra.

    January 21, 2014