metro vs railway line

metro and railway line both are nouns.

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

As nouns, railway line is a hypernym of metro; that is, railway line 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 line: 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 system.

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