bilevel railcar vs railcar

bilevel railcar and railcar both are nouns.

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

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

bilevel railcar: 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 railcar include car, railroad car, railway car.

bilevel railcar (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