hardtop vs auto

hardtop and auto both are nouns.

Word	Noun	Adjective	Verb	Adverb
hardtop	Yes	No	No	No
auto	Yes	No	No	No

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

hardtop: a car that resembles a convertible but has a fixed rigid top
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other hypernyms of hardtop include automobile, car, machine, motorcar.

hardtop (noun)	auto (noun)
a car that resembles a convertible but has a fixed rigid top	a motor vehicle with four wheels; usually propelled by an internal combustion engine