Adjective: subterranean ,súb-tu'rey-nee-un
- Being or operating under the surface of the earth
"subterranean passages";
- subterraneous
- Lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed)
"subterranean motives for murder";
- subterraneous, ulterior
See also: covert, subsurface
Encyclopedia: Subterranean