antistrophe vs introit

antistrophe

noun
  • The lines of this part of the choral song. 

  • The repetition of a word or phrase at the end of successive clauses 

  • In Greek choruses and dances, the returning of the chorus, exactly answering to a previous strophe or movement from right to left. 

  • The repetition of words in an inverse order. 

  • The retort or turning of an adversary's plea against him. 

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 

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