Noun

1. A partially shaded area around the edges of a shadow, especially an eclipse.
2. A region around the edge of a sunspot, darker than the sun's surface but lighter than the middle of the sunspot.
3. 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.
   • 1965, William O. Douglas, Griswold v. Connecticut, United States Reports, 381 U.S. 479

     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.

4. (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.

Noun

1. situation of low light