penance vs propitiation

penance

noun
  • A sacrament in some Christian churches. 

  • Any instrument of self-punishment. 

  • A voluntary self-imposed punishment for a sinful act or wrongdoing. It may be intended to serve as reparation for the act. 

verb
  • To impose penance; to punish. 

propitiation

noun
  • The death of Christ as a basis for the forgiveness of sin. 

  • The act of propitiating; placation, atonement, similar to expiation but with the added concept of appeasement of anger. 

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