Someone or something that eats, or a restaurant (as in 'greasy eater').
From Old English 'etan' (to eat) plus the agent suffix '-er'. This is one of the simplest word formations in English, dating back over a thousand years.
The word 'eater' reveals something fascinating about English: we can attach '-er' to almost any verb to create a noun for someone who does that action, which is why we can coin new words like 'binge-eater' or 'trash-eater' without anyone being confused.
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