OPPRESSO

from Bouvier's Law Dictionary, Revised 6th Ed (1856)
OPPRESSOR. One who having public authority uses it unlawfully to tyrannize 
over another; as, if he keep him in prison until he shall do something which 
he is not lawfully bound to do. 
     2. To charge a magistrate with being an oppressor, is therefore 
actionable. Stark. Sland. 185. 
    

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