ACCOMPLICE

n. partner in crime

At law, an accomplice is a person who actively participates in the commission of a crime, even though they take no part in the actual criminal offence. For example, in a bank robbery, the person who points the gun at the teller and asks for the money is guilty of armed robbery. However, anyone else directly involved in the commission of the crime, such as the lookout or the getaway car driver, is an accomplice, even though in the absence of an underlying offence keeping a lookout or driving a car would not be an offence.
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Noun
1. a person who joins with another in carrying out some plan (especially an unethical or illegal plan)
(synonym) confederate
(hypernym) assistant, helper, help, supporter
(hyponym) decoy, steerer

(n.)
An associate in the commission of a crime; a participator in an offense, whether a principal or an accessory.
  

(n.)
A cooperator.
  

one who voluntarily and intentionally joins with another person in committing a crime. You should consider such testimony with greater caution than that of an ordinary witness.

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 accessories before or after the fact.

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. 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.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.