Main entry: ulterior, subterranean, subterraneous
Definition: lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed)
Usage: subterranean motives for murder; looked too closely for an ulterior purpose in all knowledge- Bertrand Russell
Main entry: subterranean, subterraneous
Definition: being or operating under the surface of the earth
Usage: subterranean passages; a subsurface flow of water