Nasty describes something disgusting, unpleasant, or mean-spirited. A nasty smell might make you wrinkle your nose and step back, like when you open a forgotten lunch container from the bottom of your backpack. A nasty cut or bruise looks painful and ugly. Nasty weather means conditions that are particularly unpleasant: cold rain, biting wind, or both at once.

The word also describes cruel or spiteful behavior. A nasty comment is meant to hurt someone's feelings deliberately. If someone makes a nasty remark about your drawing, they're being deliberately mean rather than offering helpful criticism. A nasty look conveys hostility or contempt. When people act in nasty ways toward each other, they're choosing to be unkind.

Nasty can also describe something difficult or dangerous. A nasty problem in math class is one that's particularly tricky and frustrating. A nasty fall from a bike means a bad one that really hurts. Weather forecasters might warn about a nasty storm approaching.

The word carries a visceral quality: nasty things make you recoil, whether physically (from a nasty taste), emotionally (from nasty words), or both. It's stronger than simply “bad” or “unpleasant.” When something is nasty, it has a quality that genuinely repels you.