WordNet (r) 3.0 (2006):

police state
    n 1: a country that maintains repressive control over the people
         by means of police (especially secret police)

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "police state":
   absolute monarchy, aristocracy, autarchy, autocracy, autonomy,
   coalition government, colonialism, commonwealth,
   constitutional government, constitutional monarchy, democracy,
   dictatorship, dominion rule, duarchy, duumvirate, dyarchy,
   federal government, federation, feudal system, garrison state,
   gerontocracy, heteronomy, hierarchy, hierocracy, home rule,
   limited monarchy, martial law, meritocracy, militarism,
   military government, mob rule, mobocracy, monarchy, neocolonialism,
   ochlocracy, oligarchy, pantisocracy, patriarchate, patriarchy,
   pure democracy, regency, representative democracy,
   representative government, republic, self-determination,
   self-government, social democracy, stratocracy, technocracy,
   thearchy, theocracy, totalitarian government, totalitarian regime,
   triarchy, triumvirate, tyranny, welfare state