Definition

The place or space beneath the surface of the ground; subterranean space. A spirit raised from depth of underground. Shak.

Other Definitions

This word also has 2 other definitions:

UNDERGROUND (adjective)

1. Being below the surface of the ground; as, an underground story or apartment. 2. Done or occurring out of sight; secret. [Colloq.] Underground rai...

UNDERGROUND (adverb)

Beneath the surface of the earth.