To hurt or punish someone back in response to being hurt or wronged by them.
From Latin 'retaliare' (to return like for like), from 're-' (back) and 'talis' (such, like). The meaning has been consistent since ancient Rome: returning similar harm for harm received.
Biologists call this 'reciprocal aggression,' and it's one of the oldest survival strategies—even fish will remember which other fish attacked them and retaliate days later.
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