antiphon vs introitus

antiphon

noun
  • A devotional piece of music sung responsively. 

  • A response or reply. 

introitus

noun
  • A piece of music played before a mass; a musical introduction of any sort. 

  • The entrance to a hollow organ or canal; often specifically the entrance to the vagina. 

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