A gnat is a tiny flying insect. It is so small you may not see it until it is on your skin. Some kinds bite and leave an itchy spot; others just hang in a little cloud above grass or still water in the evening. Everyday English uses the word rather loosely — almost any minute, annoying fly in the air may get called a gnat, even when a scientist would give it another name. Because gnats are so small, people also reach for the word when they mean “almost nothing”: a worry that is “a gnat bite” next to the real problem. In Britain you may also hear the rude joke “gnat’s piss” for tea or beer that tastes weak.