lead-in vs prefatorial

lead-in

noun
  • A short phrase that begins the caption of a photograph. 

  • An introduction; something that leads into the beginning of something. 

  • A region of data at the beginning of a compact disc, holding the table of contents. 

prefatorial

adj
  • prefatory 

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