The Collaborative International Dictionary of English v.0.48:

Accomplice \Ac*com"plice\, n. [Ac- (perh. for the article a or
   for L. ad) + E. complice. See Complice.]
   [1913 Webster]
   1. A cooperator. [R.]
      [1913 Webster]

            Success unto our valiant general,
            And happiness to his accomplices!     --Shak.
      [1913 Webster]

   2. (Law) An associate in the commission of a crime; a
      participator in an offense, whether a principal or an
      accessory. "And thou, the cursed accomplice of his
      treason." --Johnson.

   Note: It is followed by with or of before a person and by in
         (or sometimes of) before the crime; as, A was an
         accomplice with B in the murder of C. Dryden uses it
         with to before a thing. "Suspected for accomplice to
         the fire." --Dryden.
         [1913 Webster]

   Syn: Abettor; accessory; assistant; associate; confederate;
        coadjutor; ally; promoter. See Abettor.
        [1913 Webster]

WordNet (r) 3.0 (2006):

accomplice
    n 1: a person who joins with another in carrying out some plan
         (especially an unethical or illegal plan) [syn:
         accomplice, confederate]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "accomplice":
   a party to, abettor, accessary, accessory, accomplice in crime,
   ally, assistant, associate, coconspirator, cohort, collaborator,
   colleague, confederate, conspirator, copartner, cotenant, fellow,
   fellow conspirator, henchman, partaker, participant, participator,
   partner, party, shareholder, sharer, socius criminis



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

ACCOMPLICE, crim. law. This term includes in its meaning, all persons who
have been concerned in the commission of a crime, all particepes crimitis,
whether they are considered in strict legal propriety, as principals in the
first or second degree, or merely as accessaries before or after the fact.
Foster, 341; 1 Russell, 21; 4 Bl. Com. 331; 1 Phil. Ev. 28; Merlin,
Repertoire, mot Complice. U. S. Dig. h.t.
     2. But in another sense, by the word accomplice is meant, one who not
being a principal, is yet in some way concerned in the commission of a
crime.  It has been questioned, whether one who was an accomplice to a
suicide can be punished as such.  A case occurred in Prussia where a
soldier, at the request of his comrade, had cut the latter in pieces; for
this he was tried capitally.  In the year 1817, a young woman named Leruth
received a recompense for aiding a man to kill himself.  He put the point of
a bistouri on his naked breast, and used the hand of the young woman to
plunge it with greater force into his bosom; hearing some noise he ordered
her away. The man receiving effectual aid was soon cured of the wound which
had been inflicted; and she was tried and convicted of having inflicted the
wound, and punished by ten years' imprisonment. Lepage, Science du Droit,
ch. 2 art. 3, Sec. 5. The case of Saul, the king of Israel, and his armor
bearer, (1 Sam. xxxi. 4,) and of David and the Amelekite, (2 Sam. i. 2-16,)
will doubtless occur to the reader.



The Devil's Dictionary (1881-1906):

ACCOMPLICE, n.  One associated with another in a crime, having guilty
knowledge and complicity, as an attorney who defends a criminal,
knowing him guilty.  This view of the attorney's position in the
matter has not hitherto commanded the assent of attorneys, no one
having offered them a fee for assenting.