hadal

adjective

1. of or relating to the greatest ocean depths, below approximately 20,000 feet (6500 meters).
2. of or relating to the biogeographic region of the ocean bottom below the abyssal zone.

adjective

1. of, relating to, or constituting the zones of the oceans deeper than abyssal: below about 6000 metres (18 000 ft)See also abyssal

1. 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).