decarchy vs vigintivirate

decarchy

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

vigintivirate

noun
  • A group of twenty people, especially (politics) a council of twenty men sharing an office or rule and particularly (historical) such an administrative council in ancient Rome. 

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