penumbras

Noun

penumbra (plural penumbras or penumbrae or (obsolete) penumbræ)

1. A partially shaded area around the edges of a shadow, especially an eclipse.
   • [A]ny penumbral fringe that may be detected cannot be well distinguished from the effects of the true penumbræ; […]1875 October, E. Neison [pseudonym; Edmund Neville Nevill], “On the Condition of the Atmospheres of the Planets”, in William Crookes, editor, The Quarterly Journal of Science, […], volume V (New...
2. A region around the edge of a sunspot, darker than the sun's surface but lighter than the middle of the sunspot.
   • The atmosphere was very clear, evidenced by the steadiness with which the mottling of the sun’s surface and the penumbræ of several spots were visible.1868 December 8, Henry Pratt, “The Transit of Mercury”, in The Astronomical Register: […], volume VII, number 73 (January 1869), London: J. D. Potter, […], →OCLC, “Correspondence” section, page 20
3. (figuratively) An area of uncertainty or intermediacy between two mutually exclusive states or categories.
   • These firms or businesses are not illegal in the strict sense, but there is a shadowy penumbra within which they live, and it is often convenient for the government to look the other way.1998, Debraj Ray, Development Economics, Princeton University Press, →ISBN, pages 346–347

   Synonyms:

   grey area

4. (figuratively) An area that lies on the edge of something; a fringe.
   • Thank God we are not all cowards, we have not all a low ambition, which would make men shades, pœnumbræ^([sic]) of their fellows.1842, [George B. Loring], England Opposed to Slavery, or Some Remarks upon “An Examination into the Real Causes of the War Against the United States, and an Appeal to the Other Powers of Europe...

   Synonyms:

   periphery, outskirt

5. 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.
   • The foregoing [United States Supreme Court] cases suggest that specific guarantees in the Bill of Rights have penumbras, formed by emanations from those guarantees that help give them life and substance.1965, William O. Douglas, Griswold v. Connecticut, United States Reports, 381 U.S. 479
6. (preceded by "ischaemic") A region of the brain that has lost only some of its blood supply, and retains structural integrity but has lost function.