hot rod vs motorcar

hot rod and motorcar both are nouns.

Word	Noun	Adjective	Verb	Adverb
hot rod	Yes	No	No	No
motorcar	Yes	No	No	No

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

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

Other hypernyms of hot rod include auto, automobile, car, machine.

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