pay off vs swap out

pay off

verb
  • To pay back; to repay. 

  • To bribe, especially to deter oversight. 

  • 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. 

  • To become worthwhile; to produce a net benefit. 

swap out

verb
  • To exchange (something) for (something else). (usually followed by with or for) 

  • To transfer (memory contents) into a swap file. 

  • To exchange (something or someone) for an unused (or less-used) equivalent. 

noun
  • Anything that is swapped out for another; an exchange. 

  • A pre-prepared food item used in place of an unfinished food item in order to cut down the overall preparation time during filming. 

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