1. [ adjective ] under the level of the ground
Synonyms: belowground

"belowground storage areas" "underground caverns"

Related terms: subsurface
2. [ noun ] (politics) a secret group organized to overthrow a government or occupation force
Synonyms: resistance
Related terms: revolutionary_group Maquis
3. [ adjective ] conducted with or marked by hidden aims or methods
Synonyms: secret undercover clandestine surreptitious hush-hush hugger-mugger on_the_quiet hole-and-corner cloak-and-dagger

"clandestine intelligence operations" "cloak-and-dagger activities" "secret missions" "surreptitious mobilization of troops" "an undercover investigation" "underground resistance"

Related terms: covert
4. [ adjective ] (military) used of independent armed resistance forces
Synonyms: guerrilla irregular guerilla

"guerrilla warfare" "partisan forces"

Related terms: partisan
5. [ adverb ] beneath the surface of the earth

"water flowing underground"

6. [ adverb ] in or into hiding or secret operation

"the organization was driven underground"

7. [ noun ] (transportation,business) electric underground railway
Synonyms: subway metro tube
Related terms: railway
Similar spelling:   undergrad