Tan″sy (?), n. [OE. tansaye, F. tanaise; cf. It. & Sp. tanaceto, NL. tanacetum, Pg. atanasia, athanasia, Gr. αθανασἴα immortality, fr. αθἄνατοσ immortal; ἀ priv. + θάνατοσ death.] 1. (Bot.) Any plant of the composite genus Tanacetum. The common tansy (T. vulgare) has finely divided leaves, a strong aromatic odor, and a very bitter taste. It is used for medicinal and culinary purposes.
2. A dish common in the seventeenth century, made of eggs, sugar, rose water, cream, and the juice of herbs, baked with butter in a shallow dish. Pepys.
Double tansy(Bot.), a variety of the common tansy with the leaves more dissected than usual. — Tansy mustard(Bot.), a plant (Sisymbrium canescens) of the Mustard family, with tansylike leaves.