adjective
of a machine or device :having controls that allow something to work or happen without being directly controlled by a person
of a gun :shooting many bullets very quickly when the trigger is pulled
[more ~; most ~] :happening or done without deliberate thought or effort
always happening because of a rule, law, previous agreement, etc.
noun
plural -ics
[count] a gun that shoots many bullets very quickly :an automatic weapon
a vehicle that changes gears by itself at different speeds :a car with automatic transmission