\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 ({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. [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.