One who causes harm or damage to someone or something; a person or thing that injures or hurts.
From harm (Old English hearm) + -er suffix denoting an agent or person who performs an action. The suffix -er has Germanic roots and is one of English's oldest word-formation patterns.
The word 'harmer' is surprisingly rare in modern English—we prefer 'attacker' or 'aggressor'—suggesting that older English valued describing someone by the harm they caused, while modern language prefers describing the action itself, revealing shifts in how we conceptualize wrongdoing.
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