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

Other Words from penumbra

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

Synonyms for penumbra


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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 The whole moon is in Earth’s penumbra, but the dimming is subtle. Leigh Morgan, al, 15 May 2022 In eastern Wisconsin the spectacle is scheduled to begin at 8:32 p.m. Sunday when the edge of the Earth's shadow, or penumbra, starts touching the moon. Paul A. Smith, Milwaukee Journal Sentinel, 14 May 2022 As Picasso’s palette became more relentlessly monochromatic, space itself seemed to squeeze these figures into more compressed forms, containing them with a dark penumbra of rich blue, as if the world could not allow them even a little air or light. Washington Post, 3 Mar. 2022 There’s a whole penumbra of horrible things that happen after. Jonathan Blitzer, The New Yorker, 22 Dec. 2021 This is made up of the time when the Moon hits the penumbra and umbra. Joshua Hawkins, BGR, 17 Nov. 2021 The penumbra is the outer edge of the Earth's shadow, lasting over six hours, and the umbra is the deepest part of the shadow, lasting 3.5 hours. Sherry Liang, CNN, 18 Nov. 2021 That’s when the penumbra, partial shadow, first becomes visible. Joe Mario Pedersen,, 18 Nov. 2021 The penumbra is the outer part of the Earth’s shadow, while the umbra is the deepest and darkest part of the shadow. Joshua Hawkins, BGR, 17 Nov. 2021 See More

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.

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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The first known use of penumbra was in 1665

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Dictionary Entries Near penumbra



penumbral lunar eclipse

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Last Updated

23 May 2022

Cite this Entry

“Penumbra.” Dictionary, Merriam-Webster, Accessed 23 May. 2022.

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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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