Definition of rue

• European strong-scented perennial herb with grey-green bitter-tasting leaves; an irritant similar to poison ivy
• leaves sometimes used for flavoring fruit or claret cup but should be used with great caution: can cause irritation like poison ivy
• 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"