Tansy \Tan"sy\, n. [OE. tansaye, F. tanaise; cf. It. & Sp. tanaceto, NL. tanacetum, Pg. atanasia, athanasia, Gr. 'aqanasi`a immortality, fr. 'aqa`natos immortal; 'a priv. + qa`natos death.] 1. (Bot.) Any plant of the composite genus {Tanacetum}. The common tansy ({Tanacetum vulgare}) has finely divided leaves, a strong aromatic odor, and a very bitter taste. It is used for medicinal and culinary purposes. [1913 Webster] 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. [Obs.] --Pepys. [1913 Webster] {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. [1913 Webster]