All 9 Uses

abyss
in
The House of Hades
(Auto-generated)

To Annabeth's left, the ground dropped off in a series of cliffs, like colossal steps leading deeper into the abyss.†
p. 35.8 *

abyss = a hole or dropoff so deep the bottom cannot be seen -- often used figuratively to imply a frightening bottomless pit
This could be just the first tiny part of the abyss, like the front steps.†
p. 48.8
Only Titans would see such a beautiful place as a potential outpost of the abyss—a hellish home away from home.†
p. 184.4
The abyss before them seemed to exhale.†
p. 364.7
The beasts' legs floated in the abyss, turning from solid to smoke as they moved.†
p. 406.1
Floating in the abyss, maybe three hundred feet below, was a doorway of black marble, leading into some sort of large room.†
p. 411.9
Geras spread his withered hands and dimmed the entire abyss.†
p. 413.2
Died of massive injuries while leaping like an idiot into the abyss of Chaos and splattering on the entry hall floor of Nyx's mansion.†
p. 415.7
The kitten landed on the ground in front of his master, then arched his back and hissed at the lord of the abyss.†
p. 518.8

Definitions:

(1) (abyss)
a hole or dropoff so deep the bottom cannot be seen -- often used figuratively to imply a frightening bottomless pit
(2) (meaning too rare to warrant focus)