A sharp, steep drop — whether it's in a stock price, a roller coaster, or a star's popularity — could be described as a precipitous one. Put simply, precipitous means perilously steep.
Look closely and you'll spot most of the word precipice (a sheer, almost vertical cliff) in precipitous. Now imagine how you'd feel standing at the edge peering over, and you'll grasp the sense of impending danger that precipitous tends to imply. Precipitous declines in sales lead to bankruptcy. Precipitous mountainside hiking trails are not for the acrophobic. It can describe an ascent, but precipitous is most often used for things going literally or figuratively downhill.