1. To annoy someone by complaining about his or her behavior, appearance, etc.: Mark's wife nags him about not cutting the lawn more often.

Jim's mother is always nagging him about his hair style.

Mary's parents are always nagging her to clean up her room.

2. To cause a person to feel worried for a long time: Brenda is is still nagged by the thought that she could have done better on the final exam in biology.