What does "nightshade" mean?

Nightshade: A common name of many species of the genus Solanum, given esp. to the Solanum nigrum, or black nightshade, a low, branching weed with small white flowers and black berries reputed to be poisonous. Deadly nightshade. Same as Belladonna (a). -- Enchanter's nightshade. See under Enchanter. -- Stinking nightshade. See Henbane. -- Three-leaved nightshade. See Trillium.