• synonyms


noun, plural pe·num·brae [pi-nuhm-bree] /pɪˈnʌm bri/, pe·num·bras.
  1. Astronomy.
    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.Compare umbra(def 3a).
    2. the grayish marginal portion of a sunspot.Compare umbra(def 3b).
  2. a shadowy, indefinite, or marginal area.
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Origin of penumbra

1660–70; < New Latin, equivalent to Latin paen- pen- + umbra shade
Related formspe·num·bral, pe·num·brous, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for penumbral

Historical Examples of penumbral

  • The line between the real and imaginary is vague and penumbral to us.

    Hills and the Sea

    H. Belloc

  • It may be that all the elements of the penumbral cone intersect the earth.

  • Isabel snuck into the guest bedroom and settled into an overstuffed armchair at a penumbral corner.

  • Strange, penumbral, characters roam the boardrooms of banks in the countries in transition.

    After the Rain

    Sam Vaknin

  • The penumbral line is marked from hour to hour on the maps given annually in the American Ephemeris.

British Dictionary definitions for penumbral


noun plural -brae (-briː) or -bras
  1. a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
  2. astronomy the lighter and outer region of a sunspot
  3. painting the point or area in which light and shade blend
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Compare umbra
Derived Formspenumbral or penumbrous, adjective

Word Origin for penumbra

C17: via New Latin from Latin paene almost + umbra shadow
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for penumbral



1660s, from Modern Latin penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from Latin pæne "almost" + umbra "shadow" (see umbrage). Related: Penumbral.

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Online Etymology Dictionary, © 2010 Douglas Harper

penumbral in Science


Plural penumbras penumbrae (pĭ-nŭmbrē)
  1. A partial shadow between regions of full shadow (the umbra) and full illumination, especially as cast by Earth, the Moon, or another body during an eclipse. During a partial lunar eclipse, a portion of the Moon's disk remains within the penumbra of Earth's shadow while the rest is darkened by the umbra. See Note at eclipse.
  2. The grayish outer part of a sunspot. Compare umbra.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.