antiphon vs plainsong

antiphon

noun
  • A devotional piece of music sung responsively. 

  • A response or reply. 

plainsong

noun
  • A form of monophonic chant in unison using the Gregorian scale, sung in various Christian churches. 

  • A plain unvarnished statement, without exaggeration. 

  • A cantus firmus or theme chosen for contrapuntal treatment; so called because often an actual fragment of plain-song. 

  • The simple notes of an air, without ornament or variation. 

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