calmness vs serenity

calmness

noun
  • The state of being calm; tranquillity; silence. 

  • The product of being calm. 

serenity

noun
  • The state of being serene; calmness; peacefulness. 

  • A lack of agitation or disturbance. 

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

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