underground
adjective
- 1
conducted with or marked by hidden aims or methods
clandestine intelligence operations
cloak-and-dagger activities behind enemy lines
- 2
under the level of the ground
belowground storage areas
underground caverns
adverb
- 1
beneath the surface of the earth
water flowing underground
- 2
in or into hiding or secret operation
the organization was driven underground
noun
- 1
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'
- 2
a secret group organized to overthrow a government or occupation force
Also useful for “underground”:Crossword— A long fill for tough grids