from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A person employed to associate with suspected individuals or groups with the purpose of inciting them to commit acts that will make them liable to punishment.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A person who secretly disrupts a group's activities from within the group; an instigator, troublemaker.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a secret agent who incites suspected persons to commit illegal acts
French : agent, agent + provocateur, instigator.(American Heritage® Dictionary of the English Language, Fourth Edition)
Borrowing from French agent provocateur (literally "provocative agent") (Wiktionary)