underground meaning and definition

UNDERGROUND noun

Definition of underground (noun)

1. a secret group organized to overthrow a government or occupation force
   • synonyms: resistance
2. 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'"
   • synonyms: metro, subway, subway system, tube

UNDERGROUND adjective

Definition of underground (adjective)

1. under the level of the ground
   • "belowground storage areas"; "underground caverns"
   • synonyms: belowground
2. 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"
   • synonyms: clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover

UNDERGROUND adverb

Definition of underground (adverb)

1. in or into hiding or secret operation
   • "the organization was driven underground"
2. beneath the surface of the earth
   • "water flowing underground"