Subterranean

a.

1.

Being or lying under the surface of the earth; situated within the earth, or under ground; as, subterranean springs; a subterraneous passage.

Adj.	1.	subterranean - being or operating under the surface of the earth; "subterranean passages"; "a subsurface flow of water" Synonyms: subterraneous
	2.	subterranean - 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 Synonyms: ulterior, subterraneous

subsurface, subterraneous