A rapid transit rail transport system, or a train in such systems, generally underground and serving a metropolitan area.
An urban rapid transit rail transport system, normally with lighter track and light trains (i.e. an S-Bahn or similar), or a train in such systems.
A metropolitan area.
metropolitan
An underground railway, especially for mass transit of people in urban areas.
An underground route for pipes, sewers, etc.
A rapid transit system, regardless of the elevation of its right of way; a metro system.
A train that runs on such an underground railway.
An underground walkway, tunnel for pedestrians (called pedestrian underpass in US).
To travel by underground railway.