choir vs opera

choir

noun
  • The part of a church where the choir assembles for song. 

  • A group of people who sing together; a company of people who are trained to sing together. 

  • One of the nine ranks or orders of angels. 

  • Set of strings (one per note) for a harpsichord. 

verb
  • To sing in concert. 

opera

noun
  • A building designed for the performance of such works; an opera house. 

  • A theatrical work, combining drama, music, song and sometimes dance. 

  • The score for such a work. 

  • Any showy, melodramatic or unrealistic production resembling an opera. 

  • A company dedicated to performing such works. 

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