Definitions of rue:

• noun:   (French) a street or road in France
• noun:   leaves sometimes used for flavoring fruit or claret cup but should be used with great caution: can cause irritation like poison ivy
• noun:   European strong-scented perennial herb with gray-green bitter-tasting leaves; an irritant similar to poison ivy
• noun:   sadness associated with some wrong done or some disappointment

  Example: "To his rue, the error cost him the game"

• verb:   feel remorse for; feel sorry for; be contrite about
• name:  A surname (rare: 1 in 50000 families; popularity rank in the U.S.: #5767)