'duel' (and by extension 'dueler') originates from Latin, specifically the word 'duellum', where 'duellum' meant 'war' or 'combat'.

'duellum' passed into Old French and Medieval Latin as forms like 'duel', then into Middle English as 'duel'; the agent suffix '-er' was added in English to form 'dueler' meaning 'one who duels'.

Initially, the root referred broadly to 'war' or 'armed conflict', but over time it narrowed to mean a formalized single combat between two persons; 'dueler' thus came to mean 'one who participates in such a contest'.