- of or having to do with an abyss
- designating or of the ecological zone (abyssal zone) along the deep ocean floor between the bathyal and hadal zones
- Abysmal; unfathomable.
- Of or relating to the great depths of the oceans.
- Of or relating to the region of the ocean bottom between the bathyal and hadal zones, from depths of approximately 2,000 to 6,000 meters (6,500 to 20,000 feet).
- (archaic) Belonging to, or resembling, an abyss; unfathomable. [First attested in the mid 17th century.]
- (geography) Of or belonging to the ocean depths, especially below 2000 metres (6500 ft): abyssal zone. [First attested in the mid 19th century.]
- (geology) Pertaining to or occurring at excessive depths in the earth's crust; plutonic. [First attested in the late 19th century.]