To pay back is to return money you borrowed. Also, to take revenge, which is a very different transaction.
The money sense splits round an object, and the noun payback is the point at which an investment has returned its cost. The revenge sense is where payback time comes from, and it is always a threat. There is a warm third use, since paying somebody back for a kindness means returning it. Repay is the formal single word for the financial sense.
1phrasepay backTo return money that was borrowed.
“He promised to pay back every penny.”
2phrasetakeTo take revenge on someone.
“She would pay back the insult eventually.”
Also accepted in games: repay
Practised in Phrasal Verbs, A Man Called Ove
First appears in chapter 5 of A Man Called Ove.
Practise this word