The giving of protection, e.g. the king gave protection to the realm, known as the *'king's peace'. The word was also used of a breach of protection owed. Others, such as a *sheriff, also had the right give the peace in the king's stead. Breaches of the latter, though serious, were liable to a lesser fine. [< OldEngl. mund = trust, protection + byrd = a duty, a charge] -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.