purgatory vs serenity

purgatory

noun
  • Any situation where suffering is endured, particularly as part of a process of redemption. 

adj
  • Tending to cleanse; expiatory. 

serenity

noun
  • A lack of agitation or disturbance. 

  • The state of being serene; calmness; peacefulness. 

  • A title given to a reigning prince or similar dignitary. 

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