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

悪習慣[akushuukan] bad habit
慣らす[narasu] to accustom
慣れ[nare] practice
慣れる[nareru] to grow accustomed (to)
慣行[kankou] customary practice

慣行取引き[kankoutorihiki] usual business practices (practises)
慣習[kanshuu] usual (historical) custom
慣性[kansei] inertia
慣用[kanyou] common
慣用句[kanyouku] idiomatic usage