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penumbra

[ pi-nuhm-bruh ]
/ pɪˈnʌm brə /
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noun, plural pe·num·brae [pi-nuhm-bree], /pɪˈnʌm bri/, pe·num·bras.
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).
a shadowy, indefinite, or marginal area: a penumbra of secrecy.
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.
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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

pentyl group, penuche, penuchle, penult, penultimate, penumbra, penumbral, penurious, penury, Penutian, Penza
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Words related to penumbra

shadow, dark, gloom, obscurity, shade, concealment, darkening, decline, diminution, dimming, extinction, obliteration, occultation, shroud, veil, adumbration, blackness, coolness, cover, darkness

How to use penumbra in a sentence

British Dictionary definitions for penumbra

penumbra
/ (pɪˈnʌmbrə) /
noun plural -brae (-briː) or -bras
a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
astronomy the lighter and outer region of a sunspot
painting the point or area in which light and shade blend
Compare umbra

Derived forms of penumbra

penumbral 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

Scientific definitions for penumbra

penumbra
[ pĭ-nŭm′brə ]
Plural penumbras penumbrae (pĭ-nŭm′brē)
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.
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.
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