abyssal abyssal /əˈbɪsəl/

adjective

1. Resembling an abyss in depth; so deep as to be unmeasurable  ( abysmal , abyssal , unfathomable )
   resembling an abyss in depth; so deep as to be unmeasurable
    The abyssal depths of the ocean
   the abyssal depths of the ocean
   
2. Relating to ocean depths from 2000 to 5000 meters  ( abyssal )
   relating to ocean depths from 2000 to 5000 meters