To slay means to kill, especially in dramatic battles or heroic stories. In medieval tales, knights would slay dragons threatening villages, and heroes would slay monsters. The word appears throughout mythology and fantasy literature: Perseus slew Medusa, Beowulf slew Grendel, and David slew Goliath with just a sling and stone.

The word carries a sense of triumph over something dangerous or evil. You wouldn't say someone slayed a mosquito (you'd just say they killed it or swatted it), but you might read about a warrior who slay a fearsome beast. It's the difference between eliminating a threat and conquering something truly formidable.

In modern slang, young people sometimes use slay completely differently: to mean performing brilliantly or looking amazing. Someone might say a singer slayed their performance or that an outfit slays. This usage is casual and trendy.

The past tense is usually slew (more traditional) or slayed (more common today). You might read that “the hero slew the dragon” in an old story, or that “she slayed the competition” in contemporary writing.