ABYSSAL

abysmal, abyssal, unfathomable

(adjective) resembling an abyss in depth; so deep as to be unmeasurable; “the abyssal depths of the ocean”

abyssal

(adjective) relating to ocean depths from 2000 to 5000 meters

Source: WordNet® 3.1

Etymology

Adjective

abyssal (not comparable)

(archaic) Belonging to, or resembling, an abyss; unfathomable. [First attested in the mid 17^th century.]

(geography) Of or belonging to the ocean depths, especially below 2000 metres (6500 ft): abyssal zone. [First attested in the mid 19^th century.]

(geology) Pertaining to or occurring at excessive depths in the earth's crust; plutonic. [First attested in the late 19^th century.]

Source: Wiktionary

A*byss"al, a. Etym: [Cf. Abysmal.]

Definition: 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.

Source: Webster’s Unabridged Dictionary 1913 Edition