despot

from WordNet (r) 3.0 (2006)

despot
    n 1: a cruel and oppressive dictator [syn: {tyrant}, {autocrat},
         {despot}]

from The Collaborative International Dictionary of English v.0.48

Despot \Des"pot\, n. [F. despote, LL. despotus, fr. Gr.
   despo`ths master, lord, the second part of which is akin to
   po`sis husband, and L. potens. See {Potent}.]
   1. A master; a lord; especially, an absolute or irresponsible
      ruler or sovereign.
      [1913 Webster]

            Irresponsible power in human hands so naturally
            leads to it, that cruelty has become associated with
            despot and tyrant.                    --C. J. Smith.
      [1913 Webster]

   2. One who rules regardless of a constitution or laws; a
      tyrant.
      [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

DESPOT. This word, in its most simple and original acceptation, signifies 
master and supreme lord; it is synonymous with monarch; but, taken in bad 
part, as it is usually employed, it signifies a tyrant. In some states, 
despot is the title given to the sovereign, as king is given in others. 
Encyc. Lond.

from Moby Thesaurus II by Grady Ward, 1.0

25 Moby Thesaurus words for "despot":
      Simon Legree, absolute monarch, absolute ruler, all-powerful ruler,
      arrogator, autarch, autocrat, caesar, commissar, czar, dictator,
      disciplinarian, driver, duce, hard master, martinet, oligarch,
      oppressor, pharaoh, slave driver, stickler, strong man, tyrant,
      usurper, warlord