penance vs purgation

penance

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

  • Any instrument of self-punishment. 

  • A sacrament in some Christian churches. 

verb
  • To impose penance; to punish. 

purgation

noun
  • The process or act of cleansing from sin or guilt. 

  • The process or act of purging, such as by the use of a purgative. 

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