1. of or relating to the greatest ocean depths, below approximately 20,000 feet (6500 meters).
  2. of or relating to the biogeographic region of the ocean bottom below the abyssal zone.

Origin of hadal

First recorded in 1955–60; Had(es) + -al1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for hadal


  1. of, relating to, or constituting the zones of the oceans deeper than abyssal: below about 6000 metres (18 000 ft)See also abyssal

Word Origin for hadal

C20: from French, from Hadés Hades
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

hadal in Science


  1. Relating to the deepest regions of the ocean, below about 6,000 m (19,680 ft). The hadal zone mostly comprises trenches that can reach depths greater than 10,000 m (32,800 ft).
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.