Other forms: failed; fails
The verb fail describes something that stops working, like brakes in a car that fail, or is found to be unacceptable, like restaurants that fail their inspection for cleanliness.
The verb fail comes from the Old French word faillir, meaning “be lacking,” “miss,” or “not succeed.” You can fail an exam, which means you didn't get at least a minimum number of points to pass. You can fail to live up to your potential, meaning you aren't able to meet expectations. When businesses fail, it means financial problems force them to close.