Definitions of bridle:

• noun:   the act of restraining power or action or limiting excess

  Example: "His common sense is a bridle to his quick temper"

• noun:   headgear for a horse; includes a headstall and bit and reins to give the rider or driver control
• verb:   respond to the reins, as of horses
• verb:   put a bridle on

  Example: "Bridle horses"