Something that is used to support or connect things, or to make something stronger. (Cambridge Dictionary)
A set of connected wires that is attached to a person’s teeth in order to make them straight. (Cambridge Dictionary)
A device fitted to something, in particular a weak or injured part of the body, to give support. (Oxford Dictionaries)
If you brace yourself for something unpleasant or difficult, you prepare yourself for it. (Collins Dictionary)
If you brace your self against something or brace part of your body against it, you press against something in order to steady your body or to avoid falling. (Collins Dictionary)
If you brace your shoulders or knees, you keep them stiffly in a particular position. (Collins Dictionary)
To brace something means to strengthen or support it with something else. (Collins Dictionary)
Brace. Your Dictionary.