1. The part of a firearm designed to provide energy to the firing pin in order to strike the primer of a cartridge. Some hammers, such as those on older revolvers, have the firing pin attached to the hammer and directly impact the primer. Others, generally on more modern designs, impact a transfer bar or mechanism to provide energy to the firing pin. The hammer of a gun does not have to be exposed or visible. For example, the Smith and Wesson 642 revolver and M1 Garand semi-automatic rifle both have internal hammers.
2. Easily confused with similar terms. For example, Hammer Time is not an appropriate usage in the context of guns. Unless you got slick moves and a pair of parachute pants capable of providing wind power for San Francisco or maybe smuggling dozens of illegal immigrants across the border. Otherwise, you can’t touch this.
Important Safety Tip: While it’s OK to cock your hammer, don’t ever hammer your… Umm. Never mind.