To rebuke means to sharply criticize someone for doing something wrong, expressing clear disapproval or disappointment in a serious tone. When a teacher rebukes a student for cheating, she makes it clear that the behavior was unacceptable and won't be tolerated.

A rebuke stings more than ordinary criticism because it carries weight and authority. A coach might rebuke players who aren't taking practice seriously. A parent might rebuke a child who was rude to a grandparent. The word suggests that someone in a position of authority or respect is delivering a stern correction.

You can also use rebuke as a noun: The principal's rebuke of the bullying made everyone understand how serious the situation was. A rebuke is meant to correct behavior, not to hurt: it says “you can do better than this, and I expect you to.”