Truel: A duel involving three combatants instead of the standard two.
Used mostly in game theory, truel was coined by mathematician Martin Shubik in a 1954 article, ""Does the Fittest Necessarily Survive?" It's a portmanteau of trio (or perhaps "three-way") and duel that assumes that duel has a root meaning "two," as in "duo." However, "duel" in fact is a shortening of an Old Latin word for "war," duellum, and truel ambiguously suggests a root of true.
Contests involving an unspecified number of participants are called N-uels in game theory (PDF).
From a film-studies quiz in the Education Life section of yesterday's New York Times:
The duel provides the most classic ending for westerns. This film ups the strategic tension by introducing the truel, a three-man gunfight.
1. "High Noon"
2. "Vera Cruz"
3. "High Plains Drifter"
4. "The Good, the Bad, and the Ugly"
(Answer after the jump.)
Answer to film quiz: 4.