pay somebody/something ↔ back phrasal verb ( see also ↑ pay )
1 . to give someone the money that you owe them SYN repay :
I’ll pay you back on Friday.
We’re paying back the loan over 15 years.
2 . to make someone suffer for doing something wrong or unpleasant
pay somebody back for something
I’ll pay Jenny back for what she did to me!