adjective

1. done without conscious thought or volition, as if mechanically
2. involuntary or reflex, as some muscle or gland action
3. 1. moving, operating, etc. by itself; regulating itself automatic machinery
   2. done with automatic equipment an automatic landing
4. Firearms
   1. using the force of the explosion of a shell to eject the empty cartridge case, place the next cartridge into the breech, and fire it, so that shots continue in rapid succession until the trigger is released
   2. semiautomatic (sense )

Etymology: < Gr automatos, self-moving, self-thinking (< autos, self + component < IE *mntos, thinking < base *men-, to think > mind, memory) + -ic

noun

1. an automatic (or, popularly, semiautomatic) firearm
2. any automatic machine
3. an automotive vehicle having a transmission that changes gears automatically