Abyssal (adjective)

Pertaining to the deepest parts of the ocean, the abyssal zone, typically below a depth of about 2000 meters.

Origin:

From the noun abyss, from latin abyssus "bottomless pit".

Examples:

1. The abyssal plain is a flat, featureless area of the seafloor.
2. Abyssal creatures are adapted to survive in the extreme conditions of the deep ocean.
3. The abyssal zone is characterized by very high pressure and very low temperatures.
4. Abyssal organisms are uniquely adapted to survive in the deep ocean.
5. The abyssal zone is the least explored part of the ocean, and much of it remains a mystery.