automatic (adj.)

"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. Meaning "done by self-acting machinery" is by 1850. In reference to a type of firearm, from 1877; specifically of machinery that imitates human-directed action from 1940.

automatic (n.)

1902, "automatic weapon," from automatic (adj.). Meaning "motorized vehicle with automatic transmission" is from 1949.

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Definitions of automatic from WordNet
automatic (adj.)
without volition or conscious control;
the automatic shrinking of the pupils of the eye in strong light
Synonyms: reflex / reflexive
automatic (adj.)
operating with minimal human intervention; independent of external control;
automatic transmission
a budget deficit that caused automatic spending cuts
automatic (adj.)
resembling the unthinking functioning of a machine;
an automatic `thank you'
Synonyms: automatonlike / machinelike / robotlike / robotic
automatic (n.)
light machine gun;
Synonyms: automatic rifle / machine rifle
automatic (n.)
a pistol that will keep firing until the ammunition is gone or the trigger is released;
Synonyms: automatic pistol