unfathomed(s = adj.all) profound, unplumbed, unsounded - situated at or extending to great depth; too deep to have been sounded or plumbed; "the profound depths of the sea"; "the dark unfathomed caves of ocean"; "unplumbed depths of the sea"; "remote and unsounded caverns"

unfathomed, adj.
1 of unascertained depth.
2 not fully explored or known.

N  depth, deepness, profundity, depression, hollow, pit, shaft, well, crater, gulf, bowels of the earth, botttomless pit, hell, soundings, depth of water, water, draught, submersion, plummet, sound, probe, sounding rod, sounding line, lead, bathymetry, sonar, side-looking sonar, bathometer, deep, deep seated, profound, sunk, buried, submerged, subaqueous, submarine, subterranean, subterraneous, subterrene, underground, bottomless, soundless, fathomless, unfathomed, unfathomable, abysmal, deep as a well, bathycolpian, benthal, benthopelagic, downreaching, yawning, knee deep, ankle deep, beyond one's depth, out of one's depth, over head and ears, mark twine, mark twain.