serenity vs stillness

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. 

stillness

noun
  • Habitual silence or quiet; taciturnity. 

  • The quality or state of being still. 

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