The Collaborative International Dictionary of English v.0.48:

Peace \Peace\, n. [OE. pees, pais, OF. pais, paiz, pes, F. paix,
   L. pax, pacis, akin to pacere, paciscere, pacisci, to make an
   agreement, and prob. also pangere to fasten. Cf. Appease,
   Fair, a., Fay, v., Fang, Pacify, Pact, Pay to
   requite.]
   A state of quiet or tranquillity; freedom from disturbance or
   agitation; calm; repose; specifically:
   (a) Exemption from, or cessation of, war with public enemies.
   (b) Public quiet, order, and contentment in obedience to law.
   (c) Exemption from, or subjection of, agitating passions;
       tranquillity of mind or conscience.
   (d) Reconciliation; agreement after variance; harmony;
       concord. "The eternal love and pees." --Chaucer.
       [1913 Webster]

   Note: Peace is sometimes used as an exclamation in commanding
         silence, quiet, or order. "Peace! foolish woman."
         --Shak.
         [1913 Webster]

   At peace, in a state of peace.

   Breach of the peace. See under Breach.

   Justice of the peace. See under Justice.

   Peace of God. (Law)
   (a) A term used in wills, indictments, etc., as denoting a
       state of peace and good conduct.
   (b) (Theol.) The peace of heart which is the gift of God.

   Peace offering.
   (a) (Jewish Antiq.) A voluntary offering to God in token of
       devout homage and of a sense of friendly communion with
       Him.
   (b) A gift or service offered as satisfaction to an offended
       person.

   Peace officer, a civil officer whose duty it is to preserve
      the public peace, to prevent riots, etc., as a polliceman,
      sheriff or constable.

   To hold one's peace, to be silent; to refrain from
      speaking.

   To make one's peace with, to reconcile one with, to plead
      one's cause with, or to become reconciled with, another.
      "I will make your peace with him." --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

peace officer
    n 1: an officer of the law [syn: lawman, law officer, peace
         officer]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "peace officer":
   G-man, John Law, MP, bailiff, beadle, beagle, bound bailiff,
   captain, catchpole, chief of police, commissioner, constable, cop,
   deputy, deputy sheriff, detective, fed, federal, flic, gendarme,
   government man, inspector, lictor, lieutenant, mace-bearer,
   marshal, mounted policeman, narc, officer, patrolman, police,
   police captain, police commissioner, police constable,
   police inspector, police matron, police officer, police sergeant,
   policeman, policewoman, portreeve, reeve, roundsman, sergeant,
   sergeant at arms, sheriff, superintendent, tipstaff, tipstaves,
   trooper