quadrumvirate vs tetralogy

quadrumvirate

noun
  • Synonym of quattuorvirate. 

tetralogy

noun
  • A group of four dramas, three tragic and one satiric, exhibited together at the festivals of Dionysus at Athens. 

  • Tetralogy of Fallot. 

  • A combination of four symptoms. 

  • A set of four works of art that are connected, and that can be seen either as a single work or as four individual works. They are commonly found in literature, film, or video games. 

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