Definition: an electric railway operating below the surface of the ground (usually in a city)
Usage: in Paris the subway system is called the `metro' and in London it is called the `tube' or the `underground'
Definition: line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight
Definition: an underground tunnel or passage enabling pedestrians to cross a road or railway
Similar words: tunnel
Definition: a passageway through or under something, usually underground (especially one for trains or cars)
Usage: the tunnel reduced congestion at that intersection