A more thorough explanation:

vadiare duellum

vadiare duellum is a Latin term used in history to describe the act of giving pledges to each other to engage in trial by combat. This means that two people would agree to fight each other to settle a dispute, and they would both promise to show up and fight.

An example of vadiare duellum would be two knights in medieval times who had a disagreement over who owned a piece of land. They might agree to vadiare duellum and fight each other with swords to determine who was right.

Another example would be two samurai in feudal Japan who had a disagreement over who should be the leader of their clan. They might agree to vadiare duellum and fight each other with swords to determine who was the better warrior and therefore the better leader.

These examples illustrate the definition of vadiare duellum because in both cases, the two parties agreed to fight each other to settle a dispute. They gave pledges to each other that they would show up and fight, and the winner would be declared the winner of the dispute.