[ pi-nuhm-bruh ]
See synonyms for penumbra on
noun,plural pe·num·brae [pi-nuhm-bree], /pɪˈnʌm bri/, pe·num·bras.
  1. Astronomy.

    • 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).

    • the grayish marginal portion of a sunspot.: Compare umbra (def. 3b).

  2. a shadowy, indefinite, or marginal area: a penumbra of secrecy.

  1. U.S. Law. a right or set of rights implicit but not expressed in the U.S. Constitution or Bill of Rights: The principle of the penumbra protects against an imperfect, or incomplete, enumeration of rights.

Origin of penumbra

First recorded in 1660–65; from New Latin penumbra (coined by Johannes Kepler in 1604), equivalent to Latin paen- prefix meaning “almost” + umbra “shade”; see pen-, umbra

Other words from penumbra

  • pe·num·bral, pe·num·brous, adjective

Words Nearby penumbra Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use penumbra in a sentence

  • Yes, both injuries are experienced during a traumatic event; however, the psychological penumbra is very different.

  • In person, Waltz is equally charming, but without the penumbra of menace that comes with having Nazi goons just outside the door.

    Tarantino's Glorious Nazi | Paul Cullum | August 16, 2009 | THE DAILY BEAST
  • It formed, as it were, a penumbra of fine shrilling, and could be heard for many streets in advance.

    The Dragon Painter | Mary McNeil Fenollosa
  • The penumbra will last quite a long time yet, but it will gradually get fainter and fainter.

    Pharaoh's Broker | Ellsworth Douglass
  • And the concert ended, and soon they were alone together in the flower-filled, fragrant penumbra of the moving carriage.

    The Devourers | Annie Vivanti Chartres

British Dictionary definitions for penumbra


/ (pɪˈnʌmbrə) /

nounplural -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

  1. painting the point or area in which light and shade blend

Origin of penumbra

C17: via New Latin from Latin paene almost + umbra shadow

Derived forms of penumbra

  • penumbral or penumbrous, adjective

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

Scientific definitions for penumbra


[ pĭ-nŭmbrə ]

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.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.