Black's Law Dictionary (2nd edition)dictionaries

Mercy

In praotioe. The arbitrament of the king or judge in punishing offenses uot directly censured by law. Jacob. So, “to be in mercy” signifies to be amerced or fined for bringing or defending an unjust snit, or to be liable to punishment in the discretion of the court

Source: Black’s Law Dictionary 2nd Ed (1910)