rueful
— Adjective
– English
～ feeling or expressing pain or sorrow for sins or offenses
ruefully
— Adverb
– English
～ in a rueful manner; "`I made a big mistake,' he said ruefully"
ruefulness
— Noun
– English
～ 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"