rental vs car rental

rental and car rental both are nouns.

Word	Noun	Adjective	Verb	Adverb
rental	Yes	Yes	No	No
car rental	Yes	No	No	No

As nouns, car rental is a hyponym of rental; that is, car rental is a word with a more specific, narrower meaning than rental:

Other hyponyms of rental include hire car, rent-a-car, self-drive, u-drive, you-drive, sublease, sublet.

rental (noun)	car rental (noun)
the act of paying for the use of something (as an apartment or house or car)	a rented car
property that is leased or rented out or let

rental (adjective)	car rental (adjective)
of or relating to rent
available to rent or lease