The Collaborative International Dictionary of English v.0.48:

Despotism \Des"po*tism\, n. [Cf. F. despotisme.]
   1. The power, spirit, or principles of a despot; absolute
      control over others; tyrannical sway; tyranny. "The
      despotism of vice." --Byron.
      [1913 Webster]

   2. A government which is directed by a despot; a despotic
      monarchy; absolutism; autocracy.
      [1913 Webster]

            Despotism . . . is the only form of government which
            may with safety to itself neglect the education of
            its infant poor.                      --Bp. Horsley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

despotism
    n 1: dominance through threat of punishment and violence [syn:
         absolutism, tyranny, despotism]
    2: a form of government in which the ruler is an absolute
       dictator (not restricted by a constitution or laws or
       opposition etc.) [syn: dictatorship, absolutism,
       authoritarianism, Caesarism, despotism, monocracy,
       one-man rule, shogunate, Stalinism, totalitarianism,
       tyranny]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "despotism":
   Caesarism, Stalinism, absolute monarchy, absolutism,
   argumentum baculinum, autarchy, authoritarianism, autocracy,
   benevolent despotism, big stick, czarism, dictatorship, domination,
   domineering, fascism, heavy hand, high hand, iron boot, iron hand,
   iron heel, kaiserism, monarchy, monocracy, one-man rule,
   one-party rule, oppression, paternalism, reign of terror,
   repression, suppression, terrorism, thought control,
   totalitarianism, tyranny



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

DESPOTISM, government. That abuse of government, where the sovereign power
is not divided, but united in the hands of a single man, whatever may be his
official title. It is not, properly, a form of government. Toull. Dr. Civ.
Fr. tit. prel. n. 32; Rutherf Inst. b. 1, c. 20, Sec. 1. Vide Tyranny;
Tyrant.