adjective
(not comparable) Below the ground; below the surface of the Earth.
(figurative) Hidden, furtive, secretive.
(of music, art etc.) Outside the mainstream, especially unofficial and hidden from the authorities.
adverb
Below the ground.
Secretly.
noun
(geography) Regions beneath the surface of the earth, both natural (eg. caves) and man-made (eg. mines).
(chiefly British) Synonym of subway: a railway that is under the ground.
(with definite article) A movement or organisation of people who resist political convention.
(with definite article) A movement or organisation of people who resist artistic convention.
verb
To route electricity distribution cables underground.
verb
simple past and past participle of undergrind