met ‧ ro /ˈmetrəʊ $ -troʊ/ BrE AmE 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