- of or relating to the greatest ocean depths, below approximately 20,000 feet (6500 meters).
- of or relating to the biogeographic region of the ocean bottom below the abyssal zone.
- of, relating to, or constituting the zones of the oceans deeper than abyssal: below about 6000 metres (18 000 ft)See also abyssal
- Relating to the deepest regions of the ocean, below about 6,000 m (19,680 ft). The hadal zone mostly comprises trenches that can reach depths greater than 10,000 m (32,800 ft).