Nefarious means wickedly evil or criminal. A nefarious plot is one designed to cause serious harm, like a scheme to steal from a charity or frame an innocent person for a crime. The word describes actions and plans that are deliberately wicked.

You might encounter nefarious in adventure stories, where villains hatch nefarious schemes to take over kingdoms or steal priceless treasures. In real life, investigators work to uncover nefarious activities like fraud or counterfeiting. The word carries a sense of sneaky, calculated wrongdoing rather than simple mischief or carelessness.

Nefarious is stronger than words like “bad” or “mean.” Breaking a rule might be bad, but plotting to hurt someone for personal gain is nefarious. The word suggests a kind of theatrical evil, which is why it appears often in stories about master criminals and their elaborate plans. When you call something nefarious, you're saying it's wickedly and intentionally wrong.