Hadal zone
The hadal zone was the ancient Greek god of the underworld. The genitive , Haidou, was an elision to denote locality: "[the house/dominion] of Hades". Eventually, the nominative came to designate the abode of the dead.In Greek mythology, Hades...

"—in other words "unseen" or "underworld"), also known as the hadopelagic zone and trench zone, is the delineation for the deepest trenches in the ocean.