subterranean Synonyms

subterraneous ulterior underground hypogean subterrene submerged submarine subereous subterrestrial subaqueous subversive subaerial tartarean tunnel in the recesses undersea underwater undercover subsurface hypogeal below ground metro belowground avant-garde undergrow underfoot sunken secret covered concealed clandestine cavernulous cavernous cavern cave buried beneath below basement covert deep profound private phreatic nether inhumed infernal igneous hypogeous hidden