noun \pə-ˈnəm-brə\
plural pen·um·brae\-(ˌ)brē, -ˌbrī\ or pen·um·bras

Definition of PENUMBRA

a :  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
:  a surrounding or adjoining region in which something exists in a lesser degree :  fringe
:  a body of rights held to be guaranteed by implication in a civil constitution
:  something that covers, surrounds, or obscures :  shroud <a penumbra of secrecy> <a penumbra of somber dignity has descended over his reputation — James Atlas>
pen·um·bral \-brəl\ adjective

Examples of PENUMBRA

  1. <the lunar eclipse began with a subtle darkening of the lunar surface as it passed within the Earth's penumbra>
  2. <a penumbra of despair fell over the doomed city>

Origin of PENUMBRA

New Latin, from Latin paene almost + umbra shadow — more at umbrage
First Known Use: 1665

Other Astronomy Terms

gibbous, nadir, nebulous, retrograde, sidereal, syzygy, wane, wax, zenith


noun \pə-ˈnəm-brə\   (Medical Dictionary)
plural pe·num·brae \-(ˌ)brē, -ˌbrī\ or pe·num·bras

Medical Definition of PENUMBRA

: a blurred area in a radiograph at the edge of an anatomical structure
pe·num·bral \-brəl\ adjective


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