Stern means serious, strict, and unsmiling. A stern teacher might look at a noisy classroom without saying a word, and suddenly everyone gets quiet. A stern warning from a parent means they're not joking around: you need to listen carefully and change your behavior.

When someone looks stern, their face shows they mean business. They're not necessarily angry, but they're definitely not amused. A coach might give her team a stern talk at halftime when they're not playing their best, speaking firmly to make sure they understand what needs to improve.

The word suggests strength and authority without being mean. A stern librarian enforces the rules about quiet voices, but she's helping everyone enjoy the library. A stern judge maintains order in the courtroom. Being stern means taking something seriously and expecting others to do the same.

Don't confuse stern with harsh or cruel. Someone can be stern while still being fair and caring. Think of it as serious determination: when your older brother gives you a stern look after you've been teasing him, he's communicating clearly that you've crossed a line, even without raising his voice.