From Greek legend. Cassandra was a Trojan princess blessed with the gift of prophecy but cursed with the fate that nobody would ever believe her. She was brought back to Greece as a captive concubine by Agamemnon, but met her death at the hands of his jealous wife Clytemnestra. Although it was never generally popular, this name was in occasional use from the Middle Ages until the 18th century, and has recently been revived by parents looking to the pages of classical mythology for distinctive names.
French (Létourneau): from Old French estournel ‘starling’ (Late Latin sturnellus, a diminutive of classical Latin sturnus), with the definite article l', hence a nickname for a chattering, gregarious person or a metonymic occupational name for a birdcatcher.