carceral vs penitential

carceral

adj
  • Of or pertaining to imprisonment or a prison. 

penitential

adj
  • Pertaining to penance or penitence 

noun
  • a book or set of rules pertaining to the Christian sacrament of penance 

How often have the words carceral and penitential occurred in a corpus of books? (source: Google Ngram Viewer )