metro vs railway system

metro and railway system both are nouns.

Word	Noun	Adjective	Verb	Adverb
metro	Yes	No	No	No
railway system	Yes	No	No	No

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

metro: an electric railway operating below the surface of the ground (usually in a city)
railway system: line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight

Other hypernyms of metro include railroad, railroad line, railway, railway line.

metro (noun)	railway system (noun)
an electric railway operating below the surface of the ground (usually in a city)	line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight