canticle vs introitus

canticle

noun
  • A chant, hymn or song, especially a nonmetrical one, with words from a biblical text. 

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 canticle and introitus occurred in a corpus of books? (source: Google Ngram Viewer )