To delude someone means to make them believe something that isn't true, usually by misleading or deceiving them. When people are deluded, they hold onto false beliefs despite evidence to the contrary. A scam artist might delude victims into thinking they've won a prize when they really haven't. A smooth-talking friend might delude you into believing they finished their homework when they're actually copying yours.

The word often suggests a kind of persistent false belief. Someone might delude themselves into thinking they're prepared for a test when they've barely studied, convincing themselves that “just looking over the notes once” was enough. This self-deception is especially common: we can delude ourselves about our abilities, our chances, or whether we've really done our best.

A delusion is the false belief itself. If someone has delusions of grandeur, they believe they're far more important or talented than they actually are, like a beginner pianist who thinks they're ready to perform at Carnegie Hall after two weeks of lessons.

The word carries a sense of being trapped in fantasy rather than seeing reality clearly. Being deluded is different from simply making a mistake: it means clinging to the false belief even when the truth is right in front of you.