From Longman Dictionary of Contemporary Englishdebaterde‧bat‧er /dɪˈbeɪtə $ -ər/ noun [countable] someone who speaks in a formal debate
Examples from the Corpus
debater• He was a debater, if not an intellectual.• Dole is a wise and experienced debater.• But is he a better-humored debater?• Though small and frail, he was a powerful and lucid debater.• He was a redoubtable debater with a caustic tongue in polemics and a nice touch in irony in writing. 