Meaning & Definition of Underground in English

1. A secret group organized to overthrow a government or occupation force

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'"

1. Under the level of the ground

• "Belowground storage areas"

• "Underground caverns"

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"

1. In or into hiding or secret operation

• "The organization was driven underground"

2. Beneath the surface of the earth

• "Water flowing underground"