choir vs serenade

choir

verb
  • To sing in concert. 

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

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

  • One of the nine ranks or orders of angels. 

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

serenade

verb
  • To sing or play a serenade for (someone). 

noun
  • A love song that is sung directly to one's love interest, especially one performed below the window of a loved one in the evening. 

  • An instrumental composition in several movements. 

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