subway
n. countable A2 Elementary US //ˈsəbˌweɪ// UK //sˈʌbweɪ// sub·way
n. an underground train system in a city. You use it to travel quickly without worrying about traffic on the streets.
n. an underground electric railway system in a city. Primarily North American in usage; in British English, the term typically refers to an underground pedestrian tunnel.
I take the subway to work every morning.
The city is expanding the subway line to reach the outer suburbs and reduce traffic congestion.
Commuters often prefer the subway during rush hour because it bypasses the gridlock that frequently paralyzes the city's main arterial roads.
From sub- + way.
Usage
Commonly used with the definite article 'the' when referring to the system as a whole.