- subterranean
- adj1. underground, hypogeal, hypo-geous, subterrestrial; below the surface, buried, sunk.2. hidden, secret, sub rosa, under wraps; concealed, ensconced, shrouded, cloaked, veiled, masked, screened, in the dark; undercover, clandestine, covert, under one's hat, furtive, backdoor, surreptitious; sly, stealthy, sneaky, sneaking, underhand, underhanded.
A Note on the Style of the synonym finder. 2014.