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 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 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). Editors, USA TODAY, "George Floyd protests, Strawberry moon, Trump visits Maine: 5 things to know Friday," 5 June 2020 As seen from Asia, Africa, and Australia, 57% of the Strawberry Moon will be covered by Earth’s penumbra — its outer, fuzzy shadow in space — and for a few hours, our bright satellite will lose its luster. Jamie Carter, Travel + Leisure, "A Strawberry Moon Eclipse Will Be Visible in Parts of the World This Week," 31 May 2020 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

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

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The first known use of penumbra was in 1665

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Statistics for penumbra

Last Updated

14 Aug 2020

Cite this Entry

“Penumbra.” Dictionary, Merriam-Webster, Accessed 20 Sep. 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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