A person or animal that starts a fight or assault against someone else.
From Old French 'atachier' (to attach/fasten), via Italian 'attaccare.' Originally meant to fasten or attach weapons, which evolved to mean engaging in combat. The '-er' suffix creates the agent noun for one who attacks.
Attack used to mean 'to fasten weapons'—people would literally attach their swords to enemies. Over centuries, the word abstracted from the physical 'fastening' to the whole concept of aggressive assault.
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