Why is the ninth month called September?
1590s, "deadly nightshade" (Atropa belladonna), from Italian, literally "fair lady;" the plant so called supposedly because women made cosmetic eye-drops from its juice (an 18c. explanation; atropic acid, found in the plant, has a well-known property of dilating the pupils) or because it was used to poison beautiful women. Perhaps a folk etymology alteration; Gamillscheg suggests ultimately of Gaulish origin.
belladonna bel·la·don·na (běl'ə-dŏn'ə)
A poisonous Eurasian perennial herb having usually solitary, purplish-brown, bell-shaped flowers and glossy black berries. Also called deadly nightshade.
An alkaloidal extract or tincture derived from this plant.