invocation vs litany

invocation

noun
  • The act or form of calling for the assistance or presence of some superior being, especially prayer offered to a divine being. 

  • The act of invoking, such as a function call. 

  • A call or summons, especially a judicial call, demand, or order. 

  • An act of invoking or claiming a legal right. 

litany

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

  • A prolonged or tedious list. 

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