passenger car vs railcar

passenger car and railcar both are nouns.

Word	Noun	Adjective	Verb	Adverb
passenger car	Yes	No	No	No
railcar	Yes	No	No	No

As nouns, railcar is a hypernym of passenger car; that is, railcar is a word with a broader meaning than passenger car:

Other hypernyms of passenger car include car, railroad car, railway car.

passenger car (noun)	railcar (noun)
a railcar where passengers ride	a wheeled vehicle adapted to the rails of railroad