railroad car vs van

railroad car and van both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad car	Yes	No	No	No
van	Yes	No	No	No

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

railroad car (noun)	van (noun)
a wheeled vehicle adapted to the rails of railroad	a truck with an enclosed cargo space
	a camper equipped with living quarters
	(Great Britain) a closed railroad car that carries baggage or freight
	the leading units moving at the head of an army
	any creative group active in the innovation and application of new concepts and techniques in a given field (especially in the arts)