One who combats; a fighter or opponent in a struggle.
From 'combat' plus the agent suffix '-er,' forming a noun for someone who performs the action of combating. This is a less common variant than 'combatant,' created through standard English word-formation rules.
English loves making '-er' nouns from verbs — 'teach' becomes 'teacher,' 'run' becomes 'runner,' 'fight' becomes 'fighter' — so 'combatter' follows an ancient pattern that's been making agent nouns for over a thousand years.
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