railway yard vs railyard

railway yard and railyard both are nouns.

Word	Noun	Adjective	Verb	Adverb
railway yard	Yes	No	No	No
railyard	Yes	No	No	No

As nouns, railway yard and railyard are synonyms defined as:

railway yard and railyard: an area having a network of railway tracks and sidings for storage and maintenance of cars and engines

Other synonyms of railway yard include yard.

railway yard (noun)	railyard (noun)
an area having a network of railway tracks and sidings for storage and maintenance of cars and engines	an area having a network of railway tracks and sidings for storage and maintenance of cars and engines