A*byss"al (?), a. [Cf. Abysmal.]
Belonging to, or resembling, an abyss; unfathomable.
Abyssal zone (Phys. Geog.), one of the
belts or zones into which Sir E. Forbes divides the bottom of the sea in
describing its plants, animals, etc. It is the one furthest from the shore,
embracing all beyond one hundred fathoms deep. Hence, abyssal
animals, plants, etc.