An electric passenger railway operated in underground tunnels.
Located below the ground level.
under the level of the ground; "belowground storage areas"; "underground caverns"
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"
used of independent armed resistance forces; "guerrilla warfare"; "partisan forces"
an electric underground railway
beneath the surface of the earth; "water flowing underground"
in or into hiding or secret operation; "the organization was driven underground"
a secret group organized to overthrow a government or occupation force
electric underground railway
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
an electric railway operating below the surface of the ground (usually in a city)
conducted with or marked by hidden aims or methods
