What does "tansy" mean?

Tansy: 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. 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.