pay off

1.  Pay the full amount on a debt or on wages, as in The car's finally paid off, or Les pays off the workers every Friday evening. [Early 1700s]
2.  Produce a profit, as in That gamble did not pay off. [Mid-1900s]
3.  Also, pay off an old score. Get revenge on someone for some grievance, require, as in Jerry was satisfied; he'd paid off his ex-partner when he bought him out at half-price, or Amy went out with her roommate's boyfriend, but she was paying off and old score.
4.  Bribe, as in The owner of the bar paid off the local police so he wouldn't get in trouble for serving liquor to minors. [Colloquial; c. 1900]

The verb has 6 meanings:

Meaning #1: yield a profit or result

Meaning #2: eliminate by paying off; as of debts
  Synonym: liquidate

Meaning #3: pay off, as of loans or promissory notes
  Synonym: redeem

Meaning #4: do or give something to somebody in return
  Synonyms: pay, make up, compensate

Meaning #5: pay someone with influence in order to receive a favor
  Synonym: buy off

Meaning #6: take vengeance on or get even
  Synonyms: pay back, get, fix