hot-rod vs auto

hot-rod and auto both are nouns.

Word	Noun	Adjective	Verb	Adverb
hot-rod	Yes	No	No	No
auto	Yes	No	No	No

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

hot-rod: a car modified to increase its speed and acceleration
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other hypernyms of hot-rod include automobile, car, machine, motorcar.

hot-rod (noun)	auto (noun)
a car modified to increase its speed and acceleration	a motor vehicle with four wheels; usually propelled by an internal combustion engine