Source : Webster's Revised Unabridged Dictionary (1913)

Rue \Rue\, n. [F. rue, L. ruta, akin to Gr. ?; cf. AS. r?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.

            Then purged with euphrasy and rue The visual nerve,
            for he had much to see.               --Milton.

            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.

   2. Fig.: Bitterness; disappointment; grief; regret.

   {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.

Rue \Rue\, n. [AS. hre['o]w. See {Rue}, v. t.]
   Sorrow; repetance. [Obs.] --Shak.

Rue \Rue\, v. t. [imp. & p. p. {Rued}; p. pr. & vb. n. {Ruing}.]
   [OE. rewen, reouwen, to grive, make sorry, AS. hre['o]wan;
   akin to OS. hrewan, D. rouwen, OHG. hriuwan, G. reun, Icel.
   hruggr grieved, hrug[eth] sorrow. [root] 18. Cf. {Ruth}.]
   1. To lament; to regret extremely; to grieve for or over.
      --Chaucer.

            I wept to see, and rued it from my heart. --Chapmen.

            Thy will Chose freely what it now so justly rues.
                                                  --Milton.

   2. To cause to grieve; to afflict. [Obs.] ``God wot, it rueth
      me.'' --Chaucer.

   3. To repent of, and withdraw from, as a bargain; to get
      released from. [Prov. Eng.]

Rue \Rue\, v. i.
   1. To have compassion. [Obs.]

            God so wisly [i. e., truly] on my soul rue.
                                                  --Chaucer.

            Which stirred men's hearts to rue upon them.
                                                  --Ridley.

   2. To feel sorrow and regret; to repent.

            Work by counsel and thou shalt not rue. --Chaucer.

            Old year, we'll dearly rue for you.   --Tennyson.

Source : WordNet®

rue
     n 1: European strong-scented perennial herb with gray-green
          bitter-tasting leaves; an irritant similar to poison ivy
          [syn: {herb of grace}, {Ruta graveolens}]
     2: leaves sometimes used for flavoring fruit or claret cup but
        should be used with great caution: can cause irritation
        like poison ivy
     3: sadness associated with some wrong done or some
        disappointment; "he drank to drown his sorrows"; "he wrote
        a note expressing his regret"; "to his rue, the error cost
        him the game" [syn: {sorrow}, {regret}, {ruefulness}]
     4: (French) a street or road in France
     v : feel remorse for; feel sorry for; be contrite about [syn: {repent},
          {regret}]