subway

subway
sub‧way /ˈsʌbweɪ/ noun [countable]1. American English a railway system that runs under the ground below a big city
   SYN  underground British English:
    the New York City subway
    a crowded subway station
    Boston has the oldest subway system in the US.
2. British English a path for people to walk under a road or railway
   SYN  underpass
     

THESAURUS

   ▪ the subway American English the railway system that runs under the ground below a big city. British people use the underground when talking about the railway system in London, and many systems outside the US: the New York subway | We got on the next subway train.
   ▪ the underground British English the railway system that runs under the ground below a big city: the London underground | an underground map | It’s quickest to travel by underground.
   ▪ the tube British English informal the railway system that runs under London: We took the tube to Trafalgar Square. | a crowded tube train
   ▪ the metro used especially to talk about the railway system that runs under Paris. Also used about some other city's systems, for example Moscow, Washington DC and Newcastle: the Paris Metro | Moscow’s metro stations