Abyss
Etymology
From Late Latin abyssus, from Greek abyssos, "bottomless," from a-, "without," plus byssos, "depth or bottom." The literal claim is that no bottom can be reached. Biblical use for the deep and for hell deepened its dread, and figurative senses — an abyss of grief or of ignorance — followed.
noun · /uh-BISS/
A bottomless or immeasurably deep chasm, literal or figurative.
What it names
A depth so great it seems to have no floor — used for physical gulfs and for overwhelming states such as despair, ruin, or the unknown.
Example
Standing at the canyon’s edge, she felt the pull of the abyss, that dizzy urge to look straight down.
Related idea
Chasm is a wide gap or gulf, often between ideas or people, but not necessarily bottomless; abyss adds unfathomable depth and a note of terror.