national anthem vs plainsong

national anthem

noun
  • The official song of a constituent state of a country. 

  • The official song of a nation or sovereign state, generally of a patriotic nature and played at events to celebrate or honor said state. 

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 national anthem and plainsong occurred in a corpus of books? (source: Google Ngram Viewer )