Pronunciation: ( —adv.,un'dur-ground'; —adj., n., v.un'dur-ground"),[key] —adv. 1. beneath the surface of the ground: traveling underground by subway. 2. in concealment or secrecy; not openly: subversion carried on underground.
—adj. 1. existing, situated, operating, or taking place beneath the surface of the ground.
2. used, or for use, underground.
3. hidden or secret; not open: underground political activities. 4. published or produced by political or social radicals or nonconformists: an underground newspaper. 5. avant-garde; experimental: an underground movie. 6. critical of or attacking the established society or system: underground opinion. 7. of or for nonconformists; unusual: an underground vegetarian restaurant.
—n. 1. the place or region beneath the surface of the ground.
2. an underground space or passage.
3. a secret organization fighting the established government or occupation forces: He fought in the French underground during the Nazi occupation of France. 4. (often cap.) a movement or group existing outside the establishment and usually reflecting unorthodox, avant-garde, or radical views.
5. Chiefly Brit.a subway system.
—v.t. to place beneath the surface of the ground: to underground utility lines.