Treat is a word with several meanings that connect around the idea of special care or enjoyment:

1. Something special that gives pleasure, especially a small gift or favorite food. A treat might be ice cream after dinner, a trip to the arcade, or staying up late on a weekend. What makes something a treat is that it's an occasional pleasure, something out of the ordinary. If you ate ice cream at every meal, it wouldn't feel like a treat anymore.
2. To behave toward someone in a particular way. When you treat people with kindness, you act considerately toward them. A bully who treats classmates poorly might ignore them, insult them, or exclude them. Parents might say, “Treat your sister the way you want to be treated,” meaning act toward her with the same respect and fairness you'd want for yourself.
3. To provide medical care for an illness or injury. Doctors treat patients by diagnosing problems and helping them heal. A nurse might treat a scraped knee by cleaning it and applying a bandage. Scientists work to develop new treatments for diseases, searching for better ways to help people recover.

The word can also mean to pay for something as a gift: “I'll treat you to lunch” means “I'll pay for your lunch as a special gesture.”