|tit for tat|
|an equivalent given in return or retaliation; blow for blow|
|[C16: from earlier tip for tap]|
Giving back exactly what one receives: “If you hit me, I'll do the same to you; it's tit for tat.”
tit for tat
Repayment in kind, retaliation, as in If he won't help with the beach clean-up, I won't run a booth at the bake sale; that's tit for tat. This term is believed to be a corruption of tip for tap, which meant "a blow for a blow." Its current form dates from the mid-1500s.