adjective
precipitous
prih-SIP-ih-tus/prɪˈsɪpɪtəs/
So steep that it suggests a sudden drop.
A narrow trail winds along the edge of a precipitous cliff.

Etymology
From French precipiteux, the adjective initially described rash haste or headlong movement. Its later application to high, steep terrain links the image of a headlong plunge with both steepness and dangerous suddenness.
In context
the ascent is precipitous but the path path is cut into continual and short windings which enable you to surmount the perpendicularity of the mountain
More examples
- The hikers avoid the precipitous slope above the river.
- The road zigzags down a precipitous mountainside.
- A sturdy railing guards the precipitous drop behind the house.
Forms
precipitous
precipitously adverb — At a very steep downward angle.