The playbill identified the high school student
as duel enrolled at the local college.

I wanted to check out the school catalog and learn more about this dueling class.
It’s highly unlikely I’d have found it.

It’s more likely I would have learned about the policies and procedures governing dual enrollment, a common practice for college-bound students. To maximize their time and minimize college costs, more and more are taking college courses while still in high school. The are dual enrolled—the term the writer of the playbill meant to write.

While the two words have some similarity, and are easily confused, they come from two different roots. Duel comes from the Latin duellem, a variant on the Roman word for war—bellum. Bellicose, antebellum, and rebel derive from it. 

For centuries, dueling was the acceptable means for two gentlemen to settle disagreements—most often an argument that challenged one’s honor or integrity. A formal set of rules governed such engagements. The combatants met on a field of honor, their confrontation often attracting spectators. The one who was challenged got to choose the weapon. The goal was not to kill, but to draw first blood. That determined guilt or innocence, the veracity of the accusation.

Dual comes from the Latin dualis, where we get duo or double. Duo or dua serves as a prefix for a set of words that refer to two: duet, duologue or the more familiar dialogue, and dualism. Dual is an adjective, thus it precedes words like enrolled, citizenship, purpose, tires.

Duel is a noun in this sentence:  Aaron Burr challenged Alexander Hamilton to a duel.

A verb in this one: The two dueled on a field of honor.

And in a rare occurrence, duel is used as an adjective. Of late, to describe the latest craze sweeping the night scene—dueling pianos. But I don’t think they ever draw blood.