WordNet (r) 3.0 (2006):

Gestapo
    n 1: the secret state police in Nazi Germany; known for its
         terrorist methods

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "Gestapo":
   Cheka, FBI, Interpol, MP, MVD, Mounties, NKVD, OGPU, RCMP, SP,
   Scotland Yard, constabulary, county police, highway patrol,
   law enforcement agency, military police, police, police force,
   political police, posse, provincial police, riot police,
   secret police, security force, shore patrol, special police,
   state police, tactical police, troopers, vigilance committee,
   vigilantes