falsetto vs mezzo-soprano

falsetto

noun
  • A person who sings in falsetto. 

  • The "false" (singing) voice in any human, usually airy and lacking a purity of vowels; created by utilizing the next highest vocal folds above those used for speech and normal range singing. It is commonly confused with the head voice register. 

verb
  • To sing or utter in falsetto. 

mezzo-soprano

noun
  • A person having such a voice. 

  • A voice or voice part intermediate in compass between soprano and contralto. 

How often have the words falsetto and mezzo-soprano occurred in a corpus of books? (source: Google Ngram Viewer )