disputant

Noun

 * 1) A participant in a dispute.
 * 2) * 1893, Henry James, Collaboration
 * One of the liveliest scenes of the performance was the evening, last winter, on which I became aware that one of my compatriots – an American, my good friend Alfred Bonus – was engaged in a controversy somewhat acrimonious, on a literary subject, with Herman Heidenmauer, the young composer who had been playing to us divinely a short time before and whom I thought of neither as a disputant nor as an Englishman.

Adjective

 * 1) Disputing; engaged in controversy.