The Collaborative International Dictionary of English v.0.48:

Gendarme \Gen`darme"\, n.; pl. Gendarmes, or Gens d'armes.
   [F.]
   1. (Mil.) One of a body of heavy cavalry. [Obs.] [France]
      [1913 Webster]

   2. An armed policeman in France. --Thackeray.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gendarme
    n 1: a French policeman

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "gendarme":
   Dogberry, G-man, John Law, MP, bailiff, beadle, beagle, bluecoat,
   bobby, bound bailiff, bull, captain, catchpole, chief of police,
   commissioner, constable, cop, copper, deputy, deputy sheriff,
   detective, dick, fed, federal, flatfoot, flattie, flic, fuzz,
   government man, gumshoe, heat, inspector, lictor, lieutenant,
   mace-bearer, marshal, mounted policeman, narc, officer, paddy,
   patrolman, peace officer, peeler, pig, police captain,
   police commissioner, police constable, police inspector,
   police matron, police officer, police sergeant, policeman,
   policewoman, portreeve, reeve, roundsman, sergeant,
   sergeant at arms, shamus, sheriff, superintendent, the cops,
   the fuzz, the law, tipstaff, tipstaves, trooper