Below the ground; below the surface of the Earth.
Hidden, furtive, secretive.
Outside the mainstream, especially unofficial and hidden from the authorities.
Below the ground.
Secretly.
To route electricity distribution cables underground.
A movement or organisation of people who resist artistic convention.
A movement or organisation of people who resist political convention.
Regions beneath the surface of the earth, both natural (eg. caves) and man-made (eg. mines).
Synonym of subway: a railway that is under the ground.
Existing, relating to, or made for use beneath the sea.