an eye for an eye
US /ən aɪ fɔr ən aɪ/
UK /ən aɪ fɔr ən aɪ/

1.
a principle of retributive justice in which punishment inflicted should be equivalent in degree and kind to the offense
:
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Some believe that an eye for an eye is the only way to achieve true justice.
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The old law of an eye for an eye often leads to endless cycles of revenge.