(n): a political unit organized to promote revolution
(n): an electric railway operating below the surface of the ground (usually in a city)
(n): line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight
(adv): in or into hiding or secret operation
(adv): beneath the surface of the earth
(adj): under the level of the ground
(adj): vs. overhead) (vs. surface) -- (beneath the surface
(adj): prenominal), hugger-mugger, hush-hush, secret, surreptitious, undercover, underground -- (conducted with or marked by hidden aims or methods
(adj): vs. overt) -- (secret or hidden; not openly practiced or engaged in or shown or avowed
