THESAURUS
abysmal
Atlantean, Brobdingnagian, Cyclopean, Gargantuan, Herculean, Homeric, abyssal, appalling, astronomic, awful, bottomless, cavernous, colossal, deep as hell, dreadful, elephantine, enormous, epic, fathomless, gaping, giant, giantlike, gigantic, heroic, huge, illimitable, immense, infinite, jumbo, mammoth, mighty, monster, monstrous, monumental, mountainous, plumbless, plunging, prodigious, profound, soundless, stupendous, terrible, titanic, towering, tremendous, unfathomable, unfathomed, unsounded, vast, without bottom, yawning
ROGET THESAURUS
abysmal
Depth
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.