penitence (n.)

"sorrow for committing sin or for having offended, with the intention of amending one's life; mortification undertaken to make amends for sin," c. 1200, from Old French penitence (11c.) and directly from Latin pænitentia "repentance" (Medieval Latin penitentia), noun of condition from pænitentum (nominative pænitens) "penitent," present participle of pænitere "cause or feel regret," probably originally "is not enough, is unsatisfactory," from pæne "nearly, almost, practically," which is of uncertain origin. The basic meaning seems to be "missing, lacking." Related: Penitency.