a person who joins with another in carrying out some plan (especially an unethical or illegal plan)
An associate in the commission of a crime; a participator in an offense, whether a principal or an accessory.
The word accomplice comes from the Old French complice, meaning "confederate," which was derived from the Latin complicāre, meaning "to fold together." Its modern spelling includes an extra 'a' due to the influence of the related word accomplish.