IPA: /ˈdjuːlər/
KK: /ˈdjuːlər/
A person who engages in a formal fight with weapons, usually to settle a dispute or challenge.
The two men were known as skilled duelers, often meeting at dawn to settle their differences.
Dueler → It is formed from "duel" (from Old French *duel*, meaning a fight or combat between two people) and "-er" (meaning a person who). A dueler is a person who engages in a duel.
Think of someone who participates in a 'fight' ('duel') — the '-er' indicates that this person is involved in that action.