pitfall

noun

Etymology: First recorded use in the 14th century from pit + fall in the sense of "pit trap, pit snare", from Old English fealle (“trap, snare”), from Proto-Germanic *fallą, *fallaz (“a fall, trap”), from Proto-Indo-European *(s)pōl-. Cognate with German Falle (“trap, snare”).

1. A potential, unsuspected, hidden problem, hazard, or danger that is easily encountered but not immediately obvious.

   “It's usually a simple task, but you should know the pitfalls before you attempt it yourself.”

2. A type of trap consisting of a concealed pit in the ground, which the victim is supposed to fall into and not be able to get out from.
3. An antipattern.
4. Subsidence below ground in a mine, which can cause the ground level above to drop.

   “This pitfall, beginning in February and finishing in May, resulted in a drop of about 3 ft. in the platform level; during this period it was necessary to level the track three times weekly, and impose a service slack of 15 m.p.h. The subsidence appears now to have finished, and normal speed is once again permitted.”