Abyss, a bottomless gulf or pit; any unfathomable (or apparently unfathomable) cavity or chasm or void extending below (often used figuratively).

ETYM Latin abyssus a bottomless gulf, from Greek for bottomless; a priv. + byssos depth, bottom.
(Irregular plural: abysses).
A bottomless gulf or pit; SYN. abysm.
Any unfathomable (or apparently unfathomable) cavity or chasm or void extending below (often used figuratively)

ETYM French précipice, Latin praecipitium, from praeceps, -cipitis, headlong; prae before + caput, capitis, the head. Related to Pre-, and Chief.
1. A very steep or overhanging place, a very steep cliff.
2. A hazardous situation; broadly; brink.