WordWeb Online

1. Under the level of the ground
   "underground caverns";
   - belowground
    
2. Conducted with or marked by hidden aims or methods
   "underground resistance";
   - clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover
    
3. (of music, art, etc) not mainstream; radically new

1. A secret group organized to overthrow a government or occupation force
   - resistance
    
2. [Brit] 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'";
   - metro, tube [UK], subway system [N. Amer], subway [N. Amer]

1. In or into hiding or secret operation
   "the organization was driven underground"
    
2. Beneath the surface of the earth
   "water flowing underground"

Derived forms: undergrounds

See also: covert, subsurface

Type of: rail, railroad [N. Amer], railroad line [N. Amer], railway [Brit, Cdn], railway line [Brit, Cdn], railway system [Brit, Cdn], revolutionary group

Encyclopedia: Underground