quartet vs trio

quartet

noun
  • A group of four people or things, particularly 

  • 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. 

trio

noun
  • A group of three people or things. 

  • A piece of music written for three musicians. 

  • A group of three musicians. 

  • Any cocktail made with a spirit, a liqueur, and a creamy ingredient. 

  • A passage in the middle of a minuet, frequently in a different key. 

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