novemvirate vs quattuorvirate

novemvirate

noun
  • A group of nine people, especially (politics) a council of nine men who share office or rule. 

quattuorvirate

noun
  • A group of four people, especially a council of four men sharing office or rule. 

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