sir vs viscount

sir

noun
  • to a knight or other low member of the peerage. 

  • A man of a higher rank or position. 

  • to a teacher. 

  • to a superior military officer. 

  • A respectful term of address to a man of higher rank or position 

  • A respectful term of address to an adult male (often older), especially if his name or proper title is unknown. 

verb
  • To address (someone) using "sir". 

viscount

noun
  • A member of the peerage, above a baron but below a count or earl. 

  • Any of various nymphalid butterflies of the genus Tanaecia. Other butterflies in this genus are called earls and counts. 

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