1. Someone who assists, encourages, instigates, or supports another person with criminal intent in attempting or carrying out a crime; often used in the phrase "aid and abet".
2. Those who encourage, or incite another person on to commit a crime: "He was an abetter wtih the thief in robbing the bank."
3. Etymology: from about 1374 (implied in abetting), from Old French abeter, "to bait, to harass with dogs"; litterally, "to cause to bite" from à, "to" + beter "to bait", from a Germanic source, perhaps Low Franconian betan, "incite" or Old Norse beita, "cause to bite".

Legally, abet is usually applied to aiding in the commission of a crime. In relation to the charge of "aiding and abetting", the term includes knowledge of the perpetrator's wrongful purpose, and encouragement, promotion or counsel of another person in the commission of the criminal offense.

An abettor is legally considered to be an instigator, or "setter on"; someone who promotes or procures a crime to be committed.