bilevel car vs railcar

bilevel car and railcar both are nouns.

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

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

bilevel car: a type of rail car that has two levels of passenger accommodation, as opposed to one, increasing passenger capacity.
railcar: a wheeled vehicle adapted to the rails of railroad

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

bilevel car (noun)	railcar (noun)
a type of rail car that has two levels of passenger accommodation, as opposed to one, increasing passenger capacity.	a wheeled vehicle adapted to the rails of railroad