/euh bis"euhl/ , adj.
1. of or like an abyss; immeasurable; unfathomable.
2. of or pertaining to the biogeographic zone of the ocean bottom between the bathyal and hadal zones: from depths of approximately 13,000 to 21,000 ft. (4000 to 6500 m).
[ 1685-95; abyssalis. See ABYSS, -AL 1 ]