Underground (1928 film)
WordNet
adjective
(1) 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"
(2) Under the level of the ground
"Belowground storage areas"
"Underground caverns"
adverb
(3) Beneath the surface of the earth
"Water flowing underground"
(4) In or into hiding or secret operation
"The organization was driven underground"
noun
(5) 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'"
(6) A secret group organized to overthrow a government or occupation force