decarchy vs myriarchy

decarchy

noun
  • A government of ten people, especially (historical) various Greek councils of ten men 

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 decarchy and myriarchy occurred in a corpus of books? (source: Google Ngram Viewer )