railcar vs cabin car

railcar and cabin car both are nouns.

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

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

railcar: a wheeled vehicle adapted to the rails of railroad
cabin car: a car on a freight train for use of the train crew; usually the last car on the train

railcar (noun)	cabin car (noun)
a wheeled vehicle adapted to the rails of railroad	a car on a freight train for use of the train crew; usually the last car on the train