Webster's Revised Unabridged Dictionary · 1913

Rue

Rue (ru) , noun

[French rue, Latin ruta, akin to Greek "ryth`; compare Anglo-Saxon rūde.]

1.
(Botany) 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.
Figuratively: Bitterness; disappointment; grief; regret.
Collocations (3)
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 (rud) , transitive verb

[Old English rewen, reouwen, to grive, make sorry, Anglo-Saxon hreówan; akin to Old Saxon hrewan, Dutch rouwen, Old High German hriuwan, German reuen, Icelandic hryggr grieved, hryge sorrow. r 18. Compare 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. [Obsolete]
God wot, it rueth me. — Chaucer
3.
To repent of, and withdraw from, as a bargain; to get released from. [Provincial English]

Rue , intransitive verb

1.
To have compassion. [Obsolete]
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

Rue , noun

[Anglo-Saxon hreów. See Rue, transitive verb]

Sorrow; repetance. [Obsolete] — Shakespeare