The Collaborative International Dictionary of English v.0.48:

Rue \Rue\ (r[udd]), n. [F. rue, L. ruta, akin to Gr. "ryth`; cf.
   AS. r[=u]de.]
   1. (Bot.) A perennial suffrutescent plant (Ruta
      graveolens), having a strong, heavy odor and a bitter
      taste; herb of grace. It is used in medicine.
      [1913 Webster]

            Then purged with euphrasy and rue
            The visual nerve, for he had much to see. --Milton.
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            They [the exorcists] are to try the devil by holy
            water, incense, sulphur, rue, which from thence, as
            we suppose, came to be called herb of grace. --Jer.
                                                  Taylor.
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   2. Fig.: Bitterness; disappointment; grief; regret.
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   Goat's rue. See under Goat.

   Rue anemone, a pretty springtime flower (Thalictrum
      anemonides) common in the United States.

   Wall rue, a little fern (Asplenium Ruta-muraria) common
      on walls in Europe.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rue anemone
    n 1: woodland flower native to eastern North America having cup-
         shaped flowers reminiscent of anemone but more delicate
         [syn: rue anemone, Anemonella thalictroides]