expound vs work out

expound

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

  • To make a statement, especially at length. 

work out

verb
  • To make sense of. 

  • To strengthen a part one’s body by exercise. 

  • To earn a wage working away from one's farm. 

  • To bring about or cause to happen by work or effort. 

  • To succeed; to result in a satisfactory situation. 

  • To conclude with the correct solution. 

  • To remove all the mineral that can be profitably exploited. 

  • To smooth or perfect. 

  • To exercise, especially by lifting weights. 

  • Used other than figuratively or idiomatically: see work, out. 

  • To calculate. 

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