Duel
1) A combat between two persons specifically : a formal combat with weapons fought between two persons in the presence of witnesses
2) A conflict between antagonistic persons, ideas, or forces also : a hard-fought contest between two opponents
Dual
1) Of grammatical number : denoting reference to two
2) Consisting of two parts or elements or having two like parts, e.g. families with dual incomes;
He held dual citizenship in France and the U.S.
3) Having a double character or nature