disputant

A participant in a dispute.

1893, Henry James, Collaboration https://web.archive.org/web/20061013012124/http://www.henryjames.org.uk/collab/CLtext.htm 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.

Disputing; engaged in controversy.

[...] [T]here was found / Among the graveſt Rabbies diſputant / On points and queſtions fitting Moſes Chair, / Teaching not taught; [...]