make a killing vs pay off

make a killing

verb
  • To win or earn a large amount of money. 

pay off

verb
  • To become worthwhile; to produce a net benefit. 

  • To bribe, especially to deter oversight. 

  • To pay back; to repay. 

  • To pay back (repay, pay off) the entirety of a loan, thereby effecting the release of a lien on. 

  • To fall to leeward, as the head of a vessel under sail. 

How often have the words make a killing and pay off occurred in a corpus of books? (source: Google Ngram Viewer )