pen·​um·​bra | \ pə-ˈnəm-brə How to pronounce penumbra (audio) \
plural penumbrae\ pə-​ˈnəm-​(ˌ)brē How to pronounce penumbra (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 penumbra (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 At that moment, the penumbra will cover 76.5 percent of the lunar disk. Joe Rao, Scientific American, "Minor Lunar Eclipse on Friday: How to See It," 17 Oct. 2013 For nearly four hours on Friday, at least some part of the southern portion of the moon will be within Earth's pale penumbra, our planet's faint outer shadow. Joe Rao, Scientific American, "Minor Lunar Eclipse on Friday: How to See It," 17 Oct. 2013 Early Monday morning, the moon entered what is called a penumbral lunar eclipse, when the moon moves into Earth's penumbra, or outer shadow. Ryan Prior, CNN, "See the lunar eclipse during the full beaver moon," 1 Dec. 2020 When does the last bit of penumbra cease to be visible? Curtis Roelle,, "Star Points: Leonid meteor shower and penumbral lunar eclipse on tap this month | COMMENTARY," 31 Oct. 2020 This full moon, which is classified as a strawberry moon, will bring a partial penumbral eclipse—in which the Earth's outer shadow, known as the penumbra, will appear on the moon's surface. Daisy Hernandez, Popular Mechanics, "How To Watch Tonight's Penumbral Eclipse," 5 June 2020 The Strawberry Moon will also showcase a penumbral lunar eclipse, which occurs when the moon passes through the Earth's penumbra, or partial shadow, causing part of the moon to look darker. Tierney Mcafee, Country Living, "Tonight's Strawberry Moon Will Be One of the Largest-Looking Full Moons of the Year," 5 June 2020 Less spectacular than 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). Editors, USA TODAY, "Fourth of July, Nathan's Famous Hot Dog Eating Contest, penumbral lunar eclipse: 5 things to know this weekend," 5 July 2020 The Earth blocks some of the sun's light from directly reaching the moon's surface, and covers all or part of the moon with the outer part of its shadow, also known as the penumbra. Elizabeth Gulino,, "The Penumbral Eclipse Will Look Subtle — But Its Effects Are Major," 2 July 2020

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

24 Mar 2021

Cite this Entry

“Penumbra.” Dictionary, Merriam-Webster, Accessed 18 Apr. 2021.

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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 penumbra (audio) , -​ˌbrī How to pronounce penumbra (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 penumbra (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 penumbra (audio) \ adjective

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