decarchy vs undecimvirate

decarchy

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

undecimvirate

noun
  • A group of eleven people, especially (politics) a council of eleven men sharing office or power and particularly (historical) the groups of eleven magistrates in ancient Athens. 

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