sovereigndom vs tetrarchy

sovereigndom

noun
  • The state, condition, or realm of a sovereign; sovereignty. 

tetrarchy

noun
  • The land ruled by such a government, either together or separately. 

  • A government where power is shared by four people, especially (historical) the Herodian tetrarchy established in Judea after the death of Herod and the Tetrarchy of Diocletian which ruled the Roman Empire in the years 293-313. 

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