Hardened means made tough, strong, or resistant through experience or treatment. When steel is hardened in a forge, it becomes stronger and less likely to break. When concrete hardens, it transforms from a wet mixture into solid stone.

The word also describes people who've become tougher through difficult experiences. A hardened soldier has seen combat and no longer flinches at danger. A hardened criminal has spent years breaking the law and feels little guilt about it. When we say someone has a hardened heart, we mean they've stopped feeling sympathy or compassion, usually because they've been hurt or disappointed so many times that they've built emotional walls to protect themselves.

You can see hardening happen in smaller ways too. When you practice piano every day, the tips of your fingers develop hardened calluses that make playing less painful. When a coach seems hardened to complaints about tough practices, it's because she's heard every excuse before and knows that hard work produces results.

The word suggests a kind of strength, but also a loss of softness or vulnerability. Something hardened is prepared for rough treatment, whether that's a hardened shell protecting a seed or a hardened attitude protecting someone's feelings.