The phrase '''smoking gun''' is an idiom that refers to utterly compelling evidence for something. The phrase relates to the notion of a detective or police officer investigating a murder and finding someone standing over the victim, holding a gun that still has smoke issuing from it. | The phrase '''smoking gun''' is an idiom that refers to utterly compelling evidence for something. The phrase relates to the notion of a detective or police officer investigating a murder and finding someone standing over the victim, holding a gun that still has smoke issuing from it. |