Origin and history of repent

"of or pertaining to punishment by law," mid-15c., from Old French peinal (12c., Modern French pénal) and directly from Medieval Latin penalis, from Latin poenalis "pertaining to punishment," from poena "punishment," from Greek poinē "blood-money, fine, penalty, punishment," from PIE *kwoina, from root *kwei- "to pay, atone, compensate" (source also of Greek timē "price, worth, honor, esteem, respect," tinein "to pay a price, punish, take vengeance;" Sanskrit cinoti "observes, notes;" Avestan kaena "punishment, vengeance;" Old Church Slavonic cena "honor, price;" Lithuanian kaina "value, price").

 late 14c., regreten, "to look back with distress or sorrowful longing; to grieve for on remembering," from Old French regreter "long after, bewail, lament someone's death; ask the help of" (Modern French regretter), from re-, intensive prefix (see re-), + -greter, which is possibly from Frankish or some other Germanic source (compare Old English grætan "to weep;" Old Norse grata "to weep, groan"), from Proto-Germanic *gretan "weep." "Not found in other Romance languages, and variously explained" [Century Dictionary].

From 1550s as "to grieve at (an event, action, revelation of facts, etc.)." Related: Regretted; regretting. Replaced Old English ofþyncan, from of- "off, away," here denoting opposition, + þyncan "seem, seem fit" (as in methinks).