decemvirate vs myriarchy

decemvirate

noun
  • A group of ten people, especially (politics) a council of ten men sharing office or power and particularly (historical) the groups of ten men who reformed and codified Roman law circa 450 BCE. 

myriarchy

noun
  • An area controlled by a Mongolian myriarch and theoretically comprising 10,000 households. 

  • A regiment of 10,000 soldiers, especially (historical) a Mongolian toman. 

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