To inject means to force a liquid into something using a needle and syringe. When a doctor injects medicine into your arm, the needle pierces your skin and pushes the liquid directly into your muscle or bloodstream. People with diabetes inject insulin every day to help their bodies process sugar. Veterinarians inject vaccines to protect pets from diseases.

Scientists might inject dye into a cell to study how it works, or mechanics might inject oil into machinery to keep it running smoothly.

In a broader sense, inject means to introduce something new into a situation, often quickly or forcefully. A teacher might inject some humor into a serious discussion to lighten the mood. A coach might inject energy into practice by introducing a fun new drill. When someone injects themselves into a conversation, they jump in, sometimes uninvited. A fresh perspective can inject new life into a stalled project.

The key idea is adding something from outside in a deliberate, focused way, whether it's medicine entering your body through a needle or enthusiasm entering a room through someone's personality.