subway vs metro

subway and metro both are nouns.

Word	Noun	Adjective	Verb	Adverb
subway	Yes	No	No	No
metro	Yes	No	No	No

As nouns, subway and metro are synonyms defined as:

subway and metro: an electric railway operating below the surface of the ground (usually in a city)

Other synonyms of subway include subway system, tube, underground.

subway (noun)	metro (noun)
an electric railway operating below the surface of the ground (usually in a city)	an electric railway operating below the surface of the ground (usually in a city)
an underground tunnel or passage enabling pedestrians to cross a road or railway