dead calm vs serenity

dead calm

noun
  • The condition of a perfectly flat sea with no waves and no wind. 

adj
  • Completely still with no waves and no wind. 

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 dead calm and serenity occurred in a corpus of books? (source: Google Ngram Viewer )