1. having the capability of starting, operating, moving, etc.,independently:

an automatic sprinkler system; an automatic car wash.
2. Physiology. occurring independently of volition, as certain muscularactions; involuntary.
3. done unconsciously or from force of habit; mechanical:

an automatic application of the brakes.
4. occurring spontaneously:

automatic enthusiasm.
5. (of a firearm, pistol, etc.) utilizing the recoil or part of the force of the explosive to eject the spent cartridge shell, introduce a new cartridge,cock the arm, and fire it repeatedly.
6. a machine that operates automatically.