悔い[kui] regret
悔いる[kuiru] to regret
悔改める[kuiaratameru] to repent
悔しさ[kuyashisa] chagrin
悔泣[kuyashinaki] crying from vexation

悔み状[kuyamijou] letter of condolence
悔む[kuyamu] to mourn
悔悟[kaigo] remorse
悔恨[kaikon] regret
後悔[koukai] regret