Meaning

noun the reappearance in a painting of an underlying image that had been painted over (usually when the later painting becomes transparent with age)

origin[Alt: A blue-tinted painting of a man's bent neck, with a faint image of a woman's face in its background] Learned borrowing from Italian pentimento (“repentance, penance, penitence; remorse; change of opinion; correction; traces of a previous image or work in an artwork”), from pentìrsi (“to repent; to regret”) + -mento (suffix forming nouns representing the actions of verbs to which it is…

Etymology from Wiktionary, CC BY-SA 3.0