From Longman Dictionary of Contemporary Englishan eye for an eyean eye for an eyeREVENGEthe idea that if someone does something wrong, you should punish them by doing the same thing to them An eye for an eye is no way to run a civilised justice system. → eye
Examples from the Corpus
an eye for an eye• The government's eye-for-an-eye justice could lead to further human rights abuses.• The Old Testament ideal of an eye for an eye speaks to that need. 