Brace can mean several related things:

When you brace yourself, you prepare your body or mind for something difficult or unpleasant. A football player braces for impact before a tackle by tensing his muscles and planting his feet. You might brace yourself before jumping into a cold swimming pool, or brace yourself emotionally before hearing disappointing news. It's that moment of gathering your strength and steadying yourself.

A brace is also something that supports or strengthens. Metal braces straighten teeth by applying steady pressure over time. A knee brace supports an injured joint. Builders use wooden braces to hold walls steady during construction. The word suggests something that holds firm against pressure or prevents collapse.

You can also use brace as a noun meaning a pair of something: a hunter might shoot a brace of pheasants, meaning two of them. This usage is less common today but appears in older books and stories.

The key idea connects all these meanings: bracing involves firmness, support, and preparation. When you brace yourself, you're creating your own internal support system. When you wear a brace, you're adding external support. Either way, you're getting ready to handle whatever force comes your way.