abyss

Etymology

From Middle English abissus, from Late Latin abyssus (“a bottomless gulf”), from Ancient Greek ἄβυσσος (ábussos, “bottomless”), from ἀ- (a-, “not”) + βυσσός (bussós, “deep place”), from βυθός (buthós, “deep place”). Displaced native Old English neowolnes.

noun

1. Hell; the bottomless pit; primeval chaos; a confined subterranean ocean.
   'You cannot enter here,' said Gandalf, and the huge shadow halted. 'Go back to the abyss prepared for you! Go back! Fall into the nothingness that awaits you and your Master. Go!' 1955, J. R. R. Tolkien, The Lord of the Rings: Return of the King, →LCCN, →OCLC, →OL, page 190
2. (frequently figurative) A bottomless or unfathomed depth, gulf, or chasm; hence, any deep, immeasurable; any void space.
   Below is the deep abyss of the Lauterbrunnen valley, and at its head a stately semi-circle of mountains, with the pyramidal Lauterbrunnen Breithorn as the centre-piece. 1960 December, Voyageur, “The Mountain Railways of the Bernese Oberland”, in Trains Illustrated, page 752
3. Anything infinite, immeasurable, or profound.
4. Moral depravity; vast intellectual or moral depth.
   They fell into the abyss of drug addiction.
5. (with article) An impending catastrophic happening.
6. (heraldry) The center of an escutcheon.
7. (oceanography) The abyssal zone.
8. (figurative) A difference, especially a large difference, between groups.