Underground
/ˈʌndəɡɹaʊnd/
noun
An underground railway, especially for mass transit of people in urban areas.
A train that runs on such an underground railway.
A rapid transit system, regardless of the elevation of its right of way.
Synonyms: Métro, metro, Tube, tube, rapid transit, underground, underground railway, underpass
noun
Regions beneath the surface of the earth, both natural (eg. caves) and man-made (eg. mines).
(with definite article) A movement or organisation of people who resist political convention.
“the French underground during World War II”
(with definite article) A movement or organisation of people who resist artistic convention.
Synonyms: avant-garde, counterculture, resistance
verb
To route electricity distribution cables underground
adjective
Below the ground; below the surface of the Earth.
“There is an underground tunnel that takes you across the river.”
Hidden, furtive, secretive.
“These criminals operate through an underground network.”
Outside the mainstream, especially unofficial and hidden from the authorities.
“underground music”
Synonyms: alternative, unconventional, hypogean, subterranean
adverb
Below the ground.
“The tunnel goes underground at this point.”
Secretly.
Synonyms: below ground, clandestinely, in secret, on the quiet