belladonna (n.) Look up belladonna at Dictionary.com
1590s, "deadly nightshade" (Atropa belladonna), from Italian, literally "fair lady" (see Bella + Donna); 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.