Roget's Thesaurus: Entry 710 (Opponent)

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#710. Opponent. -- N. opponent, antagonist, adversary; adverse party, opposition; enemy &c. 891; the other side; assailant.

oppositionist, obstructive; brawler, wrangler, brangler[obs], disputant; filibuster [U.S.], obstructionist.

malcontent; Jacobin, Fenian; demagogue, reactionist[obs].

rival, competitor.

bete noir[Fr].