contralto vs countertenor

contralto

noun
  • The lowest female voice or voice part, falling between tenor and mezzo-soprano. The terms contralto and alto refer to a similar musical pitch, but among singers, the term contralto is reserved for female singers; the equivalent male form is counter-tenor. Originally the contratenor altus was a high countermelody sung against the tenor or main melody. 

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 contralto and countertenor occurred in a corpus of books? (source: Google Ngram Viewer )