This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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adj. Situated, occurring, or operating below the surface of the earth: underground caverns; underground missile sites.

adj. Hidden or concealed; clandestine: underground resistance to the tyrant.

adj. Of or relating to an organization involved in secret or illegal activity: underground trade in weapons.

adj. Of or relating to an avant-garde movement or its films, publications, and art, usually privately produced and of special appeal and often concerned with social or artistic experiment.

n. A clandestine, often nationalist, organization fostering or planning hostile activities against, or the overthrow of, a government in power, such as an occupying military government: "an underground of dissident intellectuals” ( Kenneth L. Woodward).

n. Chiefly British A subway system.

n. An avant-garde movement or publication.

ad. Below the surface of the earth.

ad. In secret; stealthily.

v. To situate under the ground: workers undergrounding telephone lines.

adj. Below the ground; below the surface of the Earth.

adj. Hidden, furtive, secretive.

adj. Of music, art, etc, outside the mainstream.

ad. Below the ground.

ad. Secretly.

n. An underground railway.

n. A movement or organisation of people who resist political convention.

n. A movement or organisation of people who resist artistic convention.

v. To route electricity distribution cables underground

preposition. below the surface of the ground.

n. The place or space beneath the surface of the ground; subterranean space.

n. a subway or subway system, especially in the United Kingdom.

n. a secret organization opposed to the prevailing government.

n. a group or movement holding unorthodox views in an environment where conventional ideas dominate, as in artistic circles.

adj. Being below the surface of the ground.

adj. Done or occurring out of sight; secret.

ad. Beneath the surface of the earth.

n. An underground passage.

n. A contraction of underground railway.

Beneath the surface of the earth: as, to sink underground.

Being below the surface of the ground: as, an underground story or apartment.

n. That which is beneath the surface of the ground.

To place or lay underground, as an electric wire.

adj. conducted with or marked by hidden aims or methods

ad. in or into hiding or secret operation

ad. beneath the surface of the earth

adj. under the level of the ground

n. an electric railway operating below the surface of the ground (usually in a city)

n. a secret group organized to overthrow a government or occupation force

"His 1957 essay “Underground films: a bit of male truth” coined the term underground film."

covert    subsurface    underground railway   

railway line    railway    railroad line    railroad    railway system   

underground water    underground forest    underground railroad    go underground    underground railway   

secret    subterraneous    subterranean    subterrane    subterrestrial    catachthonian    hidden    clandestine    hush-hush    unconventional   

subterranean    nearby    central    vast    inner    industrial    extensive    western