pen·​um·​bra | \ pə-ˈnəm-brə How to pronounce penumbra (audio) \
plural penumbrae\ pə-​ˈnəm-​(ˌ)brē How to pronounce penumbrae (audio) , -​ˌbrī \ or penumbras

Definition of penumbra

1a : a space of partial illumination (as in an eclipse) between the perfect shadow on all sides and the full light
b : a shaded region surrounding the dark central portion of a sunspot
2 : a surrounding or adjoining region in which something exists in a lesser degree : fringe the seventeenth century lay in the penumbra of the middle ages— Edward Eggleston
3 : a body of rights held to be guaranteed by implication in a civil constitution the penumbra of the Bill of Rights
4 : something that covers, surrounds, or obscures : shroud a penumbra of secrecy a penumbra of somber dignity has descended over his reputation— James Atlas

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Other Words from penumbra

penumbral \ pə-​ˈnəm-​brəl How to pronounce penumbral (audio) \ adjective

Synonyms for penumbra


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Did You Know?

Every solar eclipse casts an umbra, the darker central area in which almost no light reaches the earth, and a penumbra, the area of partial shadow where part of the sun is still visible. Penumbra can thus be used to describe any "gray area" where things aren't all black and white. For example, the right to privacy falls under the penumbra of the U.S. Constitution; though it isn't specifically guaranteed there, the Supreme Court has held that it is implied, and thus that the government may not intrude into certain areas of a citizen's private life. Because its existence is still shadowy, however, the Court is still determining how much of an individual's life is protected by the right to privacy.

Examples of penumbra in a Sentence

the lunar eclipse began with a subtle darkening of the lunar surface as it passed within the Earth's penumbra a penumbra of despair fell over the doomed city
Recent Examples on the Web Catholicism is a dogmatic faith, but one that casts a penumbra far beyond its creed and doctrines. James Matthew Wilson, National Review, "Great American Fiction and the Catholic Literary Imagination," 16 Apr. 2020 The claim that the ERA is now part of the Constitution must also insist that there is a no-takebacks clause hiding in the penumbra of Article V. All these acrobatics are being performed for what seems like a very small prize. Ramesh Ponnuru, National Review, "The ERA Is a Zombie Amendment," 20 Feb. 2020 Not as spectacular – or noticeable – as a total lunar eclipse, a penumbral lunar eclipse is a rather subtle phenomenon that occurs when the full moon moves through the outer part of Earth’s shadow (known as the penumbra), according to Doyle Rice, USA TODAY, "Lunacy! We have 13 full moons to look forward to in 2020. Here's when you can see them.," 3 Feb. 2020 Not as spectacular as a total lunar eclipse, a penumbral lunar eclipse occurs when the moon moves through the outer part of Earth's shadow (known as the penumbra), according to Editors, USA TODAY, "Australian wildfires, wolf moon, '1917' premieres nationwide: 5 things to know Friday," 11 Jan. 2020 The eclipse on Friday will occur when the moon moves into Earth's penumbra, or outer shadow. Ashley Strickland, CNN, "Wolf moon eclipse kicks off the first of 13 full moons in 2020," 10 Jan. 2020 The event technically begins at 2:44 p.m. ET (18:44 UT) with a penumbral eclipse, when Earth’s more diffuse outer shadow, or penumbra, falls across the moon. Andrew Fazekas, National Geographic, "See a lunar eclipse on the Apollo 11 launch anniversary," 16 July 2019 The penumbra is the partial outer shadow, and the umbra is the full, dark shadow. Ashley Strickland, CNN, "Much of the world will be able to see a partial lunar eclipse Tuesday -- just not the US," 16 July 2019 Meanwhile, Lisbeth’s occasional investigative partner, the journalist Mikael Blomkvist (Sverrir Gudnason), ends up on the case as well, and back in Lisbeth’s penumbra. Alissa Wilkinson, Vox, "Lisbeth Salander returns in the limp, faux-feminist The Girl in the Spider’s Web," 9 Nov. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'penumbra.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of penumbra

1665, in the meaning defined at sense 1a

History and Etymology for penumbra

New Latin, from Latin paene almost + umbra shadow — more at umbrage

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Time Traveler for penumbra

Time Traveler

The first known use of penumbra was in 1665

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Statistics for penumbra

Last Updated

22 Apr 2020

Cite this Entry

“Penumbra.” Dictionary, Merriam-Webster, Accessed 26 May. 2020.

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More Definitions for penumbra


pe·​num·​bra | \ pə-ˈnəm-brə How to pronounce penumbra (audio) \
plural penumbrae\ -​(ˌ)brē How to pronounce penumbrae (audio) , -​ˌbrī How to pronounce penumbrae (audio) \ or penumbras

Medical Definition of penumbra

: a blurred area in a radiograph at the edge of an anatomical structure

Other Words from penumbra

penumbral \ -​brəl How to pronounce penumbral (audio) \ adjective


pe·​num·​bra | \ pi-ˈnəm-brə How to pronounce penumbra (audio) \
plural penumbras

Legal Definition of penumbra

1 : an area within which distinction or resolution is difficult or uncertain the public-private penumbra
2 : an extension of protection, reach, application, or consideration especially : a body of rights held to be guaranteed by implication from other rights explicitly enumerated in the U.S. Constitution the First Amendment has a penumbra where privacy is protected from governmental intrusion Griswold v. Connecticut, 381 U.S. 479 (1965) — see also Griswold v. Connecticut

Other Words from penumbra

penumbral \ -​brəl How to pronounce penumbral (audio) \ adjective

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