Here's how it helps determine if an unfamiliar word is about someone who wants to fight:
* "Pugnacious" means having a tendency to fight or argue.
* "Pugilist" is a boxer or someone who fights with their fists.
* "Pugnacity" is the quality of being eager or quick to fight.
So, if you encounter an unfamiliar word with "pugn-" in it, you can likely guess that it relates to fighting or aggression.