Word for the day: hadal

hadal \HEYD-l\, adjective:

1. of or pertaining to the greatest ocean depths, below approximately 20,000 feet (6500 meters).

2. of or pertaining to the biogeographic region of the ocean bottom below the abyssal zone.

Here a once-living being found the hadal current which twists in the waters of all rivers.
-- Lawrence Norfolk, The Shape of a Boar, 2000

By which I mean, if the earth itself were shrunk to the size of a lemon, the black hadal depths of even the Marianas Trench would be shallower than that moist breath of yours gathered on the lemon's skin.
-- Brad Leithauser, The Friends of Freeland, 1997

Hadal entered English in the mid-1900s, and comes from the name Hades, the Greek god of the underworld.