railcar vs carriage

railcar and carriage both are nouns.

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

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

railcar (noun)	carriage (noun)
a wheeled vehicle adapted to the rails of railroad	a vehicle with wheels drawn by one or more horses
	a railcar where passengers ride
	a machine part that carries something else
	a small vehicle with four wheels in which a baby or child is pushed around
	characteristic way of bearing one's body