Abet

ABET - To encourage or set another on to commit a crime. This word is always taken in a bad sense. To abet another to commit a murder, is to command, procure, or counsel him to commit it.

ABETTOR - One who encourages or incites, persuades or sets another on to commit a crime . Such a person is either a principal or, an accessory to the crime. When present, aiding, where a felony is committed, he is guilty as principal in the second degree, when absent he is merely an accessory.
   

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