Penumbra Definition

pĭ-nŭmbrə
penumbrae, penumbras
noun
The partly lighted area surrounding the complete shadow (umbra) of a body, as the moon, during an eclipse.
Webster's New World
The diffuse outer part of a sunspot.
American Heritage
A vague, indefinite, or borderline area.
Webster's New World
The less dark region surrounding the dark central area of a sunspot.
Webster's New World
An area in which something exists to a lesser or uncertain degree.
American Heritage
Synonyms:

Other Word Forms of Penumbra

Noun

Singular:
penumbra
Plural:
penumbrae, penumbras

Origin of Penumbra

  • From New Latin penumbra, from Latin paene (“almost") + umbra (“shadow").

    From Wiktionary

  • New Latin pēnumbra Latin paene almost Latin umbra shadow

    From American Heritage Dictionary of the English Language, 5th Edition

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penumbra