The Collaborative International Dictionary of English v.0.48:

Prosecutor \Pros"e*cu`tor\, n. [Cf. L. prosecutor an attendant.]
   1. One who prosecutes or carries on any purpose, plan, or
      business.
      [1913 Webster]

   2. (Law) The person who institutes and carries on a criminal
      suit against another in the name of the government.
      --Blackstone.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prosecutor
    n 1: a government official who conducts criminal prosecutions on
         behalf of the state [syn: prosecutor, public
         prosecutor, prosecuting officer, prosecuting attorney]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "prosecutor":
   AG, DA, KC, QC, SSC, US attorney, accusant, accuser, allegator,
   appellant, attorney general, civilian, claimant, complainant,
   corporation lawyer, court-appointed lawyer, criminal lawyer,
   defense counsel, delator, district attorney, impeacher, impugner,
   indictor, informer, junior counsel, law agent, leader, libelant,
   mouthpiece, party, petitioner, plaintiff, private attorney,
   prosecuting attorney, public prosecutor, publicist, silk,
   silk gown, solicitor general, special pleader, stuff gown,
   stuff-gownsman, suitor, the prosecution



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PROSECUTOR, practice. He who prosecutes another for a crime in the name of
the government.
     2. Prosecutors are public or private. The public prosecutor is an
officer appointed by the government, to prosecute all offences; he is the
attorney general or his deputy.
     3. A private prosecutor is one who prefers an accusation against a
party whom be suspects to be guilty. Every man may become a prosecutor, but
no man is bound except in some few of the more enormous offences, as
treason, to be one but if the prosecutor should compound a felony, he will
be guilty of a crime. The prosecutor has an inducement to prosecute, because
he cannot, in many cases, have any civil remedy until he has done his duty
to society by an endeavor to bring the offender to justice. If a prosecutor
act from proper motives, me will not be responsible to the party in damages,
though he was mistaken in his suspicions; but if, from a motive of revenge,
he institute a criminal prosecution without any reasonable foundation, he
may be punished by being mulcted in damages in an action for a malicious
prosecution.
     4. In Pennsylvania a defendant is not bound to plead to an indictment
where there is a private prosecutor, until his name shall have been indorsed
on the indictment as such, and on acquittal of the defendant, in all cases
except where the charge is for a felony, the jury may direct that he shall
pay the costs. Vide 1 Chit. Cr. Law, 1 to 10; 1 Phil. Ev. Index, h.t.; 2
Virg. Cas. 3, 20; 1 Dall. 5; 2 Bibb. 210; 6 Call. 245; 5 Rand. 669; and the
article Informer.