contralto vs viola

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. 

viola

noun
  • A stringed instrument of the violin family, somewhat larger than a violin, played under the chin, and having a deeper tone. 

  • A 10-string steel-string acoustic guitar, used in Brazilian folk music. 

  • A person who plays the viola. 

  • An organ stop having a similar tone. 

  • A berimbau viola, the smallest member of the berimbau used in capoeira music. 

  • Any of several flowering plants, of the genus Viola, including the violets and pansies. 

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