lecture vs protreptic

lecture

noun
  • A spoken lesson or exposition, usually delivered to a group. 

  • a class that primarily consists of a (weekly or other regularly held) lecture (as in sense 1) 

  • A berating or scolding. 

verb
  • To preach, to berate, to scold. 

  • To teach (somebody) by giving a speech on a given topic. 

protreptic

noun
  • A didactic speech, book, etc. 

adj
  • Serving to instruct; didactic. 

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