pen·ti·men·to 
(pĕn′tə-mĕntō)
(pĕn′tə-mĕntō)n. pl. pen·ti·men·ti (-tē)
An underlying image in a painting, especially one that has become visible when the top layer of paint has turned transparent with age, providing evidence of revision by the artist.
[Italian, correction, pentimento, from pentire, to repent, from Latin paenitēre.]