A person who disputes or argues; one who engages in disagreement or debate.
From dispute (verb) + -er (agent suffix). The -er suffix is Old English in origin and creates agent nouns meaning 'one who does X.'
English speakers added -er to nearly everything to name professions and agents—baker, teacher, player—making it one of the most common ways we create new words. A disputer is simply 'one who disputes.'
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