horseless carriage vs auto

horseless carriage and auto both are nouns.

Word	Noun	Adjective	Verb	Adverb
horseless carriage	Yes	No	No	No
auto	Yes	No	No	No

As nouns, auto is a hypernym of horseless carriage; that is, auto is a word with a broader meaning than horseless carriage:

horseless carriage: an early term for an automobile
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other hypernyms of horseless carriage include automobile, car, machine, motorcar.

horseless carriage (noun)	auto (noun)
an early term for an automobile	a motor vehicle with four wheels; usually propelled by an internal combustion engine