Quick definitions from WordNet (subterranean)
▸ adjective: lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed) ("Subterranean motives for murder")
▸ adjective: being or operating under the surface of the earth ("Subterranean passages")
▸ Also see subterranean
▸ adjective: lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed) ("Subterranean motives for murder")
▸ adjective: being or operating under the surface of the earth ("Subterranean passages")
▸ Also see subterranean