To mistreat means to treat someone or something badly, cruelly, or unfairly. When you mistreat someone, you're treating them in a way that causes real harm or suffering, whether through meanness, neglect, or abuse.

A bully mistreats classmates by targeting them day after day. Someone might mistreat a pet by not feeding it properly or leaving it outside in harsh weather. A coach who constantly insults players instead of helping them improve is mistreating the team. Workers can be mistreated by bosses who ignore safety rules or refuse to pay them fairly.

The word carries serious weight. It suggests ongoing poor treatment, not just a single mistake or moment of anger. If you snap at your brother once because you're having a terrible day, that's not great, but it's not the same as mistreating him. Mistreatment is a pattern: behavior that shows you don't respect or care about someone's well-being.