a secret group organized to overthrow a government or occupation force;
used of independent armed resistance forces; "guerrilla warfare"; "partisan forces";
conducted with or marked by hidden aims or methods; "clandestine intelligence operations"; "cloak-and-dagger activities behind enemy lines"; "hole-and-corner intrigue"; "secret missions"; "a secret agent"; "secret sales of arms"; "surreptitious mobilizati;
under the level of the ground; "belowground storage areas"; "underground caverns";
beneath the surface of the earth; "water flowing underground";
in or into hiding or secret operation; "the organization was driven underground";
