Definition of "nightshade"

Any of the poisonous plants belonging to the genus Solanum, especially black nightshade or woody nightshade.  examples

(colloquial) Any plant of the wider Solanaceae family, including the nightshades as well as tomato, potato, eggplant, and deadly nightshade.  examples

Belladonna or deadly nightshade, Atropa belladonna.  examples

Any of several plants likened to nightshade, usually because of similar dark-colored berries.  examples