quadrumvirate vs quartet

quadrumvirate

noun
  • Synonym of quattuorvirate. 

quartet

noun
  • A group of four musicians who perform classical music together. 

  • A group of four singers, usually males, who sings together in four-part harmony. 

  • A musical composition in four parts, each performed by a single voice or instrument. 

  • A group of four people or things, particularly 

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