Definition of "underground" in English

adjective

1. (not comparable) Below the ground; below the surface of the Earth.

   • There is an underground tunnel that takes you across the river.

2. (figurative) Hidden, furtive, secretive.

   • These criminals operate through an underground network.

3. (of music, art etc.) Outside the mainstream, especially unofficial and hidden from the authorities.

   • underground music

adverb

1. Below the ground.

   • The tunnel goes underground at this point.

2. Secretly.

noun

1. (geography) Regions beneath the surface of the earth, both natural (eg. caves) and man-made (eg. mines).

2. (chiefly British) Synonym of subway: a railway that is under the ground.

   • London Underground

3. (with definite article) A movement or organisation of people who resist political convention.

   • the French underground during World War II

4. (with definite article) A movement or organisation of people who resist artistic convention.

verb

1. To route electricity distribution cables underground.

verb

1. simple past and past participle of undergrind