One who duels; a person who participates in a duel.
Formed from 'duel' plus the suffix '-er' (from Old English, meaning 'one who does'). It's a straightforward agent noun describing someone who engages in dueling.
Historically, famous duelers like Andrew Jackson and Aaron Burr would have been called 'duers,' though the term itself is pretty rare because once you got good at dueling, people just called you by your name or reputation—nobody said 'that accomplished duer over there.'
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