verb (duels, duelling, duelled; US duels, dueling, dueled)[no object]
late 15th century: from Latin duellum, archaic and literary form of bellum 'war', used in medieval Latin with the meaning 'combat between two persons', partly influenced by dualis 'of two'. The original sense was 'single combat used to decide a judicial dispute'; the sense 'contest to decide a point of honour' dates from the early 17th century
Do not confuse dual with duel. Dual means 'having two parts or aspects' (the dual role of proprietor/manager), whereas duel means 'a fight or contest between two people' (he challenged me to a duel).