oration vs protreptic

oration

noun
  • A lengthy speech or argument in a private setting. 

  • A specific form of short, solemn prayer said by the president of the liturgical celebration on behalf of the people. 

  • A formal, often ceremonial speech. 

verb
  • To deliver an oration; to speak. 

protreptic

noun
  • A didactic speech, book, etc. 

adj
  • Serving to instruct; didactic. 

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