Inherited from Middle English tansy, tansey, syncopic forms of earlier tanesie, tanesei, from Old French tanesie, tanoisie, tanasie, tanaisie, from Medieval Latin tanacetum, atanacetum, attested since the 8th century, of obscure origin, speculated from Ancient Greek ἀθανασία (athanasía, “immortality”) owing to hallucinations from the thujone in the plant, else from taenia (“tapeworm”) due to its primary use against parasites by which reason it is called in Arabic حَشِيشَة الدُود (ḥašīša ad-dūd, literally “worm herb”), otherwise a Berber borrowing like tagetes.