(archaic) Belonging to, or resembling, an abyss; unfathomable. / (geography) Of or belonging to the ocean depths, especially below 2000 metres (6500 ft): abyssal zone.

Hell; the bottomless pit; primeval chaos; a confined subterranean ocean. / (frequently figuratively) A bottomless or unfathomed depth, gulf, or chasm; hence, any deep, immeasurable; any void space.

plural of abyss

Abbreviation of Abyssinia.

Abbreviation of Abyssinian.

To an abyssal, unfathomable extent.

abyssal

a large expanse of very flat and smooth ocean floor, usually found at depths of 4,600 to 5,500 meters (15,000 to 18,000 feet).

Any fish that lives below a depth of 2000 meters.

plural of abyssal rock