entreaty vs protreptic

entreaty

noun
  • The act of entreating or beseeching; a strong petition; pressing solicitation; begging. 

protreptic

noun
  • A didactic speech, book, etc. 

adj
  • Serving to instruct; didactic. 

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