from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Informal Something that serves as indisputable evidence or proof, especially of a crime: "There is no smoking gun or paper trail to [the CIA]” ( Thomas Polgar).
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Evidence, particularly of a crime, that is difficult or impossible to dispute.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. indisputable evidence (especially of a crime)
smoking + gun (Wiktionary)