Learner's definition of SUBWAY
1 chiefly US : a system of underground trains in a city
— often used before another noun
I took/rode the subway to midtown.
No one on the subway seemed to mind how crowded it was.
I've been on both the New York subway and the Underground in London.
a subway car/station
the subway platform
2 British : a road or passage for walking under a road, set of railroad tracks, etc. : underpass