railway car vs railcar

railway car and railcar both are nouns.

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

As nouns, railway car and railcar are synonyms defined as:

railway car and railcar: a wheeled vehicle adapted to the rails of railroad

Other synonyms of railway car include car, railroad car.

railway car (noun)	railcar (noun)
a wheeled vehicle adapted to the rails of railroad	a wheeled vehicle adapted to the rails of railroad