noun, plural penumbrae [pi-nuhm-bree] , penumbras.
the partial or imperfect shadow outside the complete shadow of an opaque body, as a planet, where the light from the source of illumination is only partly cut off. Compare umbra ( def 3a ).
the grayish marginal portion of a sunspot. Compare umbra ( def 3b ).
a shadowy, indefinite, or marginal area.

1660–70; < Neo-Latin, equivalent to Latin paen- pen- + umbra shade

penumbral, penumbrous, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
Cite This Source Link To penumbral
World English Dictionary
penumbra (pɪˈnʌmbrə)
n , pl -brae, -bras
1.  a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
2.  astronomy the lighter and outer region of a sunspot
3.  painting the point or area in which light and shade blend
[C17: via New Latin from Latin paene almost + umbra shadow]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
Cite This Source
Word Origin & History

1666, from Mod.L. penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from L. pæne "almost" + umbra "shadow" (see umbrage).
Online Etymology Dictionary, © 2010 Douglas Harper
Cite This Source
American Heritage
Science Dictionary
penumbra   (pĭ-nŭm'brə)  Pronunciation Key 
Plural penumbras or penumbrae (pĭ-nŭm'brē)
  1. A partial shadow between regions of full shadow (the umbra) and full illumination, especially as cast by Earth, the Moon, or another body during an eclipse. During a partial lunar eclipse, a portion of the Moon's disk remains within the penumbra of Earth's shadow while the rest is darkened by the umbra. See Note at eclipse.

  2. The grayish outer part of a sunspot. Compare umbra.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
Cite This Source
Copyright © 2014, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature