introit vs national anthem

introit

noun
  • A composition of vocal music sung at the opening of a church service. 

  • A prayer, typically part of a psalm or other portion of the Bible, read or sung at the start of Mass while or immediately after the priest ascends to the altar. 

  • An anthem or psalm sung before a Communion service 

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. 

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