n. 1. The place or space beneath the surface of the ground; subterranean space. [ 1913 Webster ]
A spirit raised from depth of underground. Shak. [ 1913 Webster ]
2. a subway or subway system, especially in the United Kingdom. [ chiefly British ] [ PJC ]
3. a secret organization opposed to the prevailing government; as, the French underground during the Nazi occupation. [ PJC ]
4. a group or movement holding unorthodox views in an environment where conventional ideas dominate, as in artistic circles. [ PJC ]
a. 1. Being below the surface of the ground; as, an underground story or apartment. [ 1913 Webster ]
2. Done or occurring out of sight; secret. [ Colloq. ] [ 1913 Webster ]
Underground railroad or Underground railway. See under Railroad. [ 1913 Webster ]
adv. Beneath the surface of the earth. [ 1913 Webster ]
. Wildcat insurance. [ Webster 1913 Suppl. ]