railyard vs railway yard

railyard and railway yard both are nouns.

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

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

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

Other synonyms of railyard include yard.

railyard (noun)	railway yard (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