A whisker is one of the long, stiff hairs that grow near the mouth of cats, dogs, mice, seals, and many other mammals. These specialized hairs are incredibly sensitive touch sensors that help animals navigate in the dark, judge whether spaces are wide enough to squeeze through, and detect nearby movement. A cat's whiskers are so sensitive they can feel tiny changes in air currents, helping the cat hunt even when it can't see well.

The word also describes something very close or narrow. When someone wins a race by a whisker, they barely won at all, maybe crossing the finish line just a fraction of a second ahead. If you come within a whisker of solving a puzzle, you almost figured it out, but not quite.

People sometimes use whiskers to mean a man's facial hair, especially the hair on the cheeks or sideburns, though this usage sounds old-fashioned today. You might read about a sea captain with impressive whiskers in a historical novel, meaning he had a bushy beard or prominent sideburns.