PENUMBRA

penumbra

(noun) a fringe region of partial shadow around an umbra

Source: WordNet® 3.1

Etymology

Noun

penumbra (plural penumbras or penumbrae)

A partially shaded area around the edges of a shadow, especially an eclipse.

(astronomy) A region around the edge of a sunspot, darker than the sun's surface but lighter than the middle of the sunspot.

(figuratively) An area of uncertainty or intermediacy between two mutually exclusive states or categories.

(figuratively) An area that lies on the edge of something; a fringe.

Something related to, connected to, and implied by, the existence of something else that is necessary for the second thing to be full and complete in its essential aspects.

(medicine) (in "ischaemic penumbra", after a stroke) A region of the brain that has lost only some of its blood supply, and retains structural integrity but has lost function.

Synonyms

• (area of uncertainty or intermediacy): grey area

• (area that lies on the edge of something): periphery, outskirt

Source: Wiktionary

Pe*num"bra, n. Etym: [NL., fr. L. paene almost + umbra shade.]

1. An incomplete or partial shadow.

2. (Astron.)

Definition: The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light. Sir I. Newton.

Note: The faint shade surrounding the dark central portion of a solar spot is also called the penumbra, and sometimes umbra.

3. (Paint.)

Definition: The part of a picture where the shade imperceptibly blends with the light.

Source: Webster’s Unabridged Dictionary 1913 Edition