underground
/ˈʌndɚˌgraʊnd/
noun
undergroundnoun
/ˈʌndɚˌgraʊnd/метрополитен
a system of trains that run below the ground in a big city
  • We took the underground to the museum.
  • Is there an underground in your city?
From the textA quick and easy way to get to different places in the city is to use an Underground train.