1. Verb: To repeatedly urge or annoy someone to do something. This is the most common meaning. For example:
* "My mom keeps nagging me to clean my room."
* "He's always nagging about the dishes."
2. Noun: A person who nags.
* "She's a real nag."
* "He's a nag about his car."
3. Noun: A tool used in carpentry. This is less common, but it refers to a tool used for shaping wood.
4. Archaic: To bark or whine. This usage is very old and rarely used today.
If you can provide more context about how "nag" is being used, I can give you a more precise definition.