1. (

• subterranean ,
• subterraneous

) being or operating under the surface of the earth; "subterranean passages"; "a subsurface flow of water" ;

2. (

• subterranean ,
• subterraneous ,
• ulterior

) lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed); "subterranean motives for murder"; "looked too closely for an ulterior purpose in all knowledge"- Bertrand Russell ;