underground

(s) under the level of the ground
- belowground storage areas
- underground caverns
belowground,
(r) in or into hiding or secret operation
- the organization was driven underground
(s) 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 mobilization of troops
- an undercover investigation
- underground resistance
clandestine, cloak-and-dagger, hush-hush, undercover, hole-and-corner, hugger-mugger, secret, surreptitious,
(r) beneath the surface of the earth
- water flowing underground

(n) a secret group organized to overthrow a government or occupation force resistance,
(n) an electric railway operating below the surface of the ground (usually in a city)
- in Paris the subway system is called the "metro" and in London it is called the "tube" or the "underground"
metro, subway, subway system, tube,

resistance belowground metro subway subway system tube clandestine cloak-and-dagger hush-hush undercover hole-and-corner hugger-mugger secret surreptitious

underground press Underground Railroad Underground Railway