litany vs refrain

litany

noun
  • A prolonged or tedious list. 

  • A ritual liturgical prayer in which a series of prayers recited by a leader are alternated with responses from the congregation. 

refrain

noun
  • A much repeated comment, complaint, or saying. 

  • The chorus or burden of a song repeated at the end of each verse or stanza. 

verb
  • To stop oneself from some action or interference; to abstain. 

  • To abstain from (food or drink). 

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