1. (

• metro ,
• tube ,
• underground ,
• subway_system ,
• subway

) an electric railway operating below the surface of the ground (usually in a city); "in Paris the subway system is called the `metro' and in London it is called the `tube' or the `underground'" ;

2. (

• underpass ,
• subway ,

) an underground tunnel or passage enabling pedestrians to cross a road or railway ;