Source : Webster's Revised Unabridged Dictionary (1913)

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 ({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.

Source : WordNet®

tansy mustard
     n : North American herb with bitter-tasting pinnate leaves
         resembling those of tansy [syn: {Descurainia pinnata}]