railroad siding vs sidetrack

railroad siding and sidetrack both are nouns.

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

As nouns, railroad siding and sidetrack are synonyms defined as:

railroad siding and sidetrack: a short stretch of railroad track used to store rolling stock or enable trains on the same line to pass

Other synonyms of railroad siding include siding, turnout.

railroad siding (noun)	sidetrack (noun)
a short stretch of railroad track used to store rolling stock or enable trains on the same line to pass	a short stretch of railroad track used to store rolling stock or enable trains on the same line to pass

railroad siding (verb)	sidetrack (verb)
	wander from a direct or straight course