Superstitious describes a belief in chance or magic. If you're superstitious, you may avoid walking under ladders, spilling salt, or passing black cats — all because you think they will bring you bad luck.
Plenty of people don't think of themselves as superstitious, yet they may do things like knock on wood or refuse to open an umbrella indoors. Or they believe their team will win if they wear their lucky socks. These actions are all superstitious, demonstrating a belief based on magic or luck rather than on reason. The Latin word that superstitious comes from is superstitionem, excessive fear of the gods.