1. shade; shadow.
2. the invariable or characteristic accompaniment or companion of a person or thing.
3. Astronomy.
. a. the complete or perfect shadow of an opaque body, as a planet, where the direct light from the source of illumination is completely cut off. Compare penumbra ( def. 1a ) .
. b. the dark central portion of a sunspot. Compare penumbra ( def. 1b ) .
4. a phantom or shadowy apparition, as of someone or something not physically present; ghost; spectral image.