railroad siding vs railway

railroad siding and railway both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad siding	Yes	No	No	No
railway	Yes	No	No	No

As nouns, railway is a hypernym of railroad siding; that is, railway is a word with a broader meaning than railroad siding:

railroad siding: a short stretch of railroad track used to store rolling stock or enable trains on the same line to pass
railway: a line of track providing a runway for wheels

Other hypernyms of railroad siding include railroad, railroad track.

railroad siding (noun)	railway (noun)
a short stretch of railroad track used to store rolling stock or enable trains on the same line to pass	line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight
	a line of track providing a runway for wheels