The difference between Auto and Automatic

When used as nouns, auto means an automobile, whereas automatic means a car with automatic transmission.

When used as adjectives, auto means automatic, whereas automatic means capable of operating without external control or intervention.

check bellow for the other definitions of Auto and Automatic

Auto as an adjective:

automatic

Examples:

"It's an auto sedan which we picked up from a wholesaler locally."

Auto as a noun (chiefly, [[attributive]]ly):

An automobile.

Examples:

"My brother is an auto mechanic."
Auto as a noun:

A setting for automatic operation.

Examples:

"Put it on auto."
Auto as a noun:

A writ.
Auto as a noun:

An automatic gearbox / transmission.

Examples:

"A body coloured centre pillar signalled the arrival of an electronic four-speed auto, slight suspension revisions and minor trim changes."
Auto as a noun:

A car with an automatic gearbox / transmission.

Examples:

"It wasn't too bad but we did hire an auto (couldn't imagine changing gears with my right hand)."

Auto as a noun (India):

An autorickshaw.

Examples:

"... users are often unable to note down the number of the taxi or the auto as the driver will just zoom past."

Automatic as an adjective:

Capable of operating without external control or intervention.

Examples:

"The automatic clothes washer was a great labor-saving device."
Automatic as an adjective:

Done out of habit or without conscious thought.

Examples:

"The reaction was automatic: flight!"
Automatic as an adjective (of a [[firearm]] such as a [[machine gun]]):

Firing continuously as long as the trigger is pressed until ammunition is exhausted.

Examples:

"Fully automatic weapons cannot be legally owned by private citizens in the US, except in very special circumstances, as by private security companies."
Automatic as an adjective (of a [[handgun]]):

An autoloader; a semi-automatic or self-loading pistol, as opposed to a revolver or other manually actuated handgun, which fires one shot per pull of the trigger; distinct from machine guns.

Examples:

"The US Army adopted John Browning's M1911 pistol as its [[sidearm]], chambered in .45 ACP (Automatic Colt Pistol)."
Automatic as an adjective (computing, of a local [[variable]]):

Automatically added to and removed from the stack during the course of function calls.
Automatic as an adjective (maths, of a group):

Having one or more finite-state automata

Automatic as a noun:

A car with automatic transmission.

Examples:

"I never learned to drive a stick. I can only drive an automatic."
Automatic as a noun:

A semi-automatic pistol.

Examples:

"The [[G-men]] raiding the [[speakeasy]] were equipped with .45 automatics, while the local policemen were carrying revolvers and shotguns."