automatic (n.) Look up automatic at Dictionary.com
"automatic weapon," 1902, from automatic (adj.). Meaning "motorized vehicle with automatic transmission" is from 1949.
automatic (adj.) Look up automatic at Dictionary.com
"self-acting, moving or acting on its own," 1812 (automatical is from 1580s; automatous from 1640s), from Greek automatos of persons "acting of one's own will;" of things "self-moving, self-acting," used of the gates of Olympus and the tripods of Hephaestus (also "without apparent cause, by accident"), from autos "self" (see auto-) + matos "thinking, animated," *men- (1) "to think."

Of involuntary animal or human actions, from 1748, first used in this sense by English physician and philosopher David Hartley (1705-1757). Meaning "done by self-acting machinery" is by 1872. In reference to a type of firearm, from 1877; specifically of machinery that imitates human-directed action from 1940.