so wrong or hurtful that it cannot or should not be forgiven; extremely bad.
Combination of 'un-' (not) and 'forgivable' (able to be forgiven), from Old English 'forgifan' meaning 'to give up' or 'pardon'. The 'give' root in forgive refers to giving up your anger.
When we forgive, we're literally 'giving away' our anger—it comes from an Old English word that meant 'to give up'. So unforgivable means you won't give up your hurt, making it one of the most serious judgments we can make.
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