underground

adverb

1. beneath the surface of the ground: traveling underground by subway.
2. in concealment or secrecy; not openly: subversion carried on underground.

adjective

3. existing, situated, operating, or taking place beneath the surface of the ground.
4. used, or for use, underground.
5. hidden or secret; not open: underground political activities.
6. published or produced by political or social radicals or nonconformists: an underground newspaper.
7. avant-garde; experimental: an underground movie.
8. critical of or attacking the established society or system: underground opinion.
9. of or for nonconformists; unusual: an underground vegetarian restaurant.

noun

10. the place or region beneath the surface of the ground.
11. an underground space or passage.
12. a secret organization fighting the established government or occupation forces: He fought in the French underground during the Nazi occupation of France.
13. (often initial capital letter) a movement or group existing outside the establishment and usually reflecting unorthodox, avant-garde, or radical views.
14. Chiefly British. a subway system.

verb (used with object)

15. to place beneath the surface of the ground: to underground utility lines.

adjective (ˈʌndəˌɡraʊnd)

1. occurring, situated, or used below ground levelan underground tunnel; an underground explosion
2. secret; hiddenunderground activities

adverb (ˌʌndəˈɡraʊnd)

3. going below ground levelthe tunnel led underground
4. into hiding or secrecythe group was driven underground

noun (ˈʌndəˌɡraʊnd)

5. a space or region below ground level
6. 1. a movement dedicated to overthrowing a government or occupation forces, as in the European countries occupied by the German army in World War II
   2. (as modifier)an underground group
7. the underground an electric passenger railway operated in underground tunnelsUS and Canadian equivalent: subway
8. (usually preceded by the)
   1. any avant-garde, experimental, or subversive movement in popular art, films, music, etc
   2. (as modifier)the underground press; underground music

adv.1570s, “below the surface,” from under + ground (n.). As an adjective, attested from c.1600; figurative sense of “hidden, secret” is attested from 1630s; adjectival meaning “subculture” is from 1953, from World War II application to resistance movements against German occupation, on analogy of the dominant culture and Nazis. Noun sense of “underground railway” is from 1887 (shortened from phrase underground railway, itself attested from 1834).