expound vs lucubrate

expound

verb
  • To set out the meaning of; to explain or discuss at length 

  • To make a statement, especially at length. 

lucubrate

verb
  • To work or write like a scholar. 

  • To work diligently by artificial light; to study at night. 

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