met‧ro /ˈmetrəʊ $ -troʊ/ noun (plural metros) [countable]
[Date: 1900-2000; Language: French; Origin: métro, from (chemin de fer) métropolitain 'metropolitan railway']
a railway system that runs under the ground below a city:
the Paris Metro
It’ll be quicker to go on the metro.
a metro station

[TahlilGaran] Dictionary of Contemporary English ▲

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

[TahlilGaran] English Thesaurus ▲