duel has 1 distinct synonym spread across 1 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a prearranged fight with deadly weapons by two people (accompanied by seconds) in order to settle a quarrel over a point of honor
any struggle between two skillful opponents (individuals or groups)
Synonyms, antonyms and the broader and narrower relations for duel come from Princeton University’s WordNet. Full sources and licences.
fight a duel, as over one's honor or a woman
“In the 19th century, men often dueled over small matters”