(2) A really crappy .45 caliber gun. I wouldn't recommend actually using one unless you, for some reason, end up lost in the Old West. Or Hollywood.
(3) Someone who makes peace, or solves a conflict.
(1) P1: I got the new Green Day album today! P2: Me too! It's amazing! P1: What's your favorite track? P2: Peacemaker, definitely! P1: I liked East Jesus Nowhere. *both get into long discussion over what song is best, eventually listing each and every track on the damned CD* (I am guilty of this as well)
(2) Old western movies sometimes use peacemakers, but some don't. The ones that don't are the ones you always see with someone shooting repeatedly into the sky for no reason. They would have to reload after every shot, but you never see that. They just got modern guns and put them in the old west. But does anyone care? No. Why? Hollywood says it's true, it must be true! Bastards.
(3) Person: Help! Help! There's a fight! Someone call the peacemaker!