The conical shadow projected from a planet or satellite, on the side opposite to the sun, within which a spectator could see no portion of the sun's disk; -- used in contradistinction from penumbra. See Penumbra.
- A dark area, especially the blackest part of a shadow from which all light is cut off. See Synonyms at shade.
- Astronomy The completely dark portion of the shadow cast by the earth, moon, or other body during an eclipse.
- Astronomy The darkest region of a sunspot.