A brace is a support that helps to steady or strengthen, and to brace is to prepare for something hard. So brace yourself for that impromptu meeting with your boss if you haven't been performing well.
We all know the braces that straighten teeth and keep injured knees in line. But in verb form, brace means to bolster or steady. “Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather,” said John Ruskin, the English writer and cultural critic. He means the wind supports us with its uplifting powers — although those living in tornado country might disagree.