Other forms: subways
A subway is the city railway that runs in tunnels under the streets. You go down the steps, tap through the barrier, and a train comes out of the dark every few minutes.
Subway is the American word for it. Londoners say the Underground or the Tube, Paris and much of Europe say metro, and Glasgow says Subway again. Then comes the trap: in Britain a subway is a pedestrian tunnel that takes you under a busy road, with no trains in it at all. So "take the subway" is a train in New York and a short damp walk under a roundabout in Birmingham. You ride the subway, take the subway, catch a subway train, and the stops are subway stations.
1nounsubwayAn underground urban railway (American English).
“We took the subway uptown and walked back through the park.”
synonyms: metro, underground, tube
2nountunnelA tunnel for people on foot, passing under a road or railway (British English).
“The subway under the ring road smelled of damp.”
Too few real examples of this word to estimate which sense is commonest.
subway is an underground railway.
Also accepted in games: metro, underground, tube
Subway is a plain compound: sub- stuck on to way, a way that runs under. Nothing more clever than that — which is exactly why English speakers on two continents were able to build different things out of the same word.
From sub + way.
Etymology from Wiktionary, CC BY-SA