adjective , adverb , noun
■ adjective / ˈʌndəgraʊnd; NAmE -dərg-/ [ only before noun ]
1.
under the surface of the ground :
underground passages / caves / streams
underground cables
—compare overground
2.
operating secretly and often illegally, especially against a government :
an underground resistance movement
■ adverb / ˌʌndəˈgraʊnd; NAmE -dərˈg-/
1.
under the surface of the ground :
Rescuers found victims trapped several feet underground.
toxic waste buried deep underground
2.
in or into a secret place in order to hide from the police, the government, etc. :
He went underground to avoid arrest.
■ noun /ˈʌndəgraʊnd; NAmE -dərg-/
1.
(often the Underground ) ( BrE ) ( NAmE sub·way ) [ sing. ] an underground railway / railroad system in a city :
underground stations
the London Underground
I always travel by underground.
—compare metro , tube
2.
the underground [ sing.+ sing./pl. v . ] a secret political organization, usually working against the government of a country
••
BRITISH / AMERICAN
underground / subway / metro / tube
A city's underground railway / railroad system is usually called the underground (often the Underground ) in BrE and the subway in NAmE . Speakers of BrE also use subway for systems in American cities and metro for systems in other European countries. The Metro is the name for the systems in Paris and Washington, D.C. London's system is often called the Tube .