repentant (adj.)

c. 1300, repenten, "be grieved over one's past and seek forgiveness; feel such regret for sins, crimes, or omissions as produces amendment of life," from Old French repentir (11c.), from re-, here perhaps used as an intensive prefix, "very much" (see re-), + Vulgar Latin *penitire "to regret," from Latin poenitire "make sorry," from poena (see penal).

The distinction between regret (q.v.) and repent is made in many modern languages, but is absent in older periods. To repent is to regret so deeply as to change the mind or course of conduct in consequence and develop new mental and spiritual habits. Also from c. 1300 in Middle English and after in an impersonal reflexive sense, especially as (it) repenteth (me, him, etc.).

And it repented the LORD that he had made man on the earth, and it grieved him at his heart.

[Genesis vi.6, KJV, 1611]

Related: Repented; repenting.

late 14c., from un- (1) "not" + repentant (adj.).