Precipice
Etymology
From Latin praecipitium, "a steep place, a fall," from praeceps, "headlong, steep," from prae-, "before, forth," plus caput, "head." The buried image is of going head-first over an edge. English kept both the physical cliff and the metaphor of standing at the brink of ruin, one move from plunging.
noun · /PRESS-ih-piss/
A very steep cliff edge, or the brink of a dangerous or disastrous situation.
What it names
The dangerous edge just before a fall — literal or figurative — where one more step means catastrophe.
Example
The two nations stood at the precipice of war, waiting to see who would step back first.
Related idea
Brink names any critical edge or verge, dramatic or mild; precipice adds the sheer vertical drop and the sense that the fall would be steep and irreversible.