abyssal

/əˈbɪsəl/

Definitions of abyssal

1. adjective

   relating to ocean depths from 2000 to 5000 meters
2. adjective

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

   synonyms: abysmal, unfathomable

   deep

   having great spatial extension or penetration downward or inward from an outer surface or backward or laterally or outward from a center; sometimes used in combination