Sir vs duchess

Sir

noun
  • The titular prefix given to a knight or baronet. 

duchess

noun
  • The wife or widow of a duke. 

  • The female ruler of a duchy. 

verb
  • to court or curry favour for political or business advantage; to flatter obsequiously. 

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