belladonna n.

1590s, "deadly nightshade" (Atropa belladonna), in Gerard's herbal. From Italian, literally "fair lady" (see belle + Donna) which name is first recorded in the works of Andrea Matthioli (1501 - ca. 1577) as herba bella donna.

Common explanations are that the plant is so called because women made cosmetic eye-drops from its juice (a mid-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 (a mid-19c. explanation).

It is more likely to be a folk etymology for one or more plants in the nightshade family, written variously in Latin as besulidus, belbulidus, belulidus, or belhulidus. Luigi Anguillara (ca. 1517 - 1570) also gives the Italian name biasola to the same plant described by Matthioli.

The term belladonna was picked up by John Gerard (ca. 1545 - 1612) who most likely acquired it from reading Matthioli. This word largely displaced the native English names for the plant, dwale (Old English dwola, see dull) and morelle (Old French morele, from Latin morella "black nightshade.") See also nightshade.