bilevel rail car vs railcar

bilevel rail car and railcar both are nouns.

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

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

bilevel rail 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 rail car include car, railroad car, railway car.

bilevel rail 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