alto vs countertenor

alto

noun
  • A musical part or section higher than tenor and lower than soprano, formerly the part that performed a countermelody above the tenor or main melody. 

  • A person or musical instrument that performs the alto part. 

  • An alto saxophone 

countertenor

noun
  • a part or section performing a countermelody against the tenor or main part 

  • male singing voice far higher than the typical male vocal range 

  • adult male singer who uses head tone or falsetto to sing far higher than the typical male vocal range 

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