Real Dictionary

rue
verb: If you rue something that you have done, you are sorry that you did it, because it has had unpleasant results.

rue in American English 1
sorrow, repentance, or regret
to be sorrowful or regretful
to feel remorse or repentance for (a sin, fault, etc.)
intransitive verb: to feel sorrow, repentance, or regret
noun: sorrow; repentance; regret
transitive verb: to feel sorrow over; repent of; regret bitterly

rue in American English 2
any of a genus (Ruta) of strong-scented shrubs of the rue family, esp. an herb (R. graveolens) with yellow flowers and bitter-tasting leaves formerly used in medicine
designating a family (Rutaceae, order Sapindales) of woody dicotyledonous plants, including the gas plant and the citrus plants
noun: any strongly scented plant of the genus Ruta, esp. R. graveolens, having yellow flowers and leaves formerly used in medicine

rue in British English 1
noun: sorrow, pity, or regret
verb: to feel sorrow, remorse, or regret for (one's own wrongdoing, past events with unpleasant consequences, etc)

rue in British English 2
noun: any rutaceous plant of the genus Ruta, esp R. graveolens, an aromatic Eurasian shrub with small yellow flowers and evergreen leaves which yield an acrid volatile oil, formerly used medicinally as a narcotic and stimulant