To fire a gun (military slang from the days of percussion cap and ball firearms before the manufacture of individual cartidges consisting of a metal casing holding a bullet, gunpowder and a primer that fired when struck by a firing pin or hammer.)

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

This is not a new phrase as much of the Rap culture would like us to believe. Instead it is an old phrase to shoot someone. Reference to cap is a word for powder cap used in percussion guns popular in the old west. This phrase is used in the 1969 movie titled "True Grit" with John Wayne, Glen Campbell, Dennis Hopper and Robert Duvall.

A slang phrase referring to the posession and use to a certain individial of a firearm or any other object resembling a firearm that emits any sort of a projectile.

Attested in "True Grit" by Charles Portis, 1968, but most likely much older.

The derivation is probably from the percussion "cap," a small metal cylinder open at one end with an amount of shock-sensitive explosive, usually fulminate of mercury, used to set off the powder charge in a muzzle-loading firearm.

The modern derivation, however, is probably from the "cap gun," a toy firearm using paper "caps" containing Armstrong's mixture or a similar substance to provide the small explosions.

To discharge a handgun, usually a 9mm, in the direction of an enemy or a rival gang.