Penitent means feeling and showing regret for wrongdoing. Look penitent, a penitent sinner, not remotely penitent.
The showing is half of it, which is why the word suits confession and courtrooms alike. In the church a penitent is the person making a confession, and penance is what follows. Repentant is the commoner everyday word.
1adjectivepenitentFeeling and showing regret for wrongdoing.
“The penitent boy apologised to his teacher and promised never to lie again.”
penitent is a state.
Latin paenitens comes from paenitere, to cause regret. Penance and repent are relatives.
Proto-Indo-European
*peh₁-
Latin
paenitēns
English, today
penitent
Built from
From Middle English -, from Old French -, from Latin paenitēns, poenitēns (“penitent”), present participle of paeniteō, poeniteō (“to cause to repent; to regret, repent”). a doublet of penitente.
Etymology from Wiktionary, CC BY-SA