WordNet (r) 3.0 (2006):

military police
    n 1: a military corps that enforces discipline and guards
         prisoners [syn: military police, MP]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "military police":
   Cheka, FBI, Gestapo, Interpol, MP, MVD, Mounties, NKVD, OGPU, RCMP,
   SP, Scotland Yard, constabulary, county police, highway patrol,
   law enforcement agency, 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