a/the smoking gun
Indisputably incriminating evidence. Likened to a gun that is still smoking after having been fired. A smoking gun was revealed in the form of emails documenting the man's involvement in the money laundering scheme. So far the prosecutor has presented only circumstantial evidence, but she's expected to reveal a smoking gun against the defendant soon.
the smoking gun
Fig. the indisputable sign of guilt. (Fig. on a murderer being caught just after shooting the victim.) Mr. south was left holding the smoking gun. The chief of staff decided that the the aide should be found with the smoking gun.
Something that serves as indisputable evidence or proof, especially of a crime. For example, There is no smoking gun in the Oval Office; the President had no role in tampering with the evidence . This expression alludes to the smoke coming from a recently discharged firearm, a normal occurrence until the invention of smokeless powder. [Mid-1900s]
a smoking gun
COMMON If you talk about a smoking gun, you mean a piece of evidence which proves that a particular person is definitely responsible for a crime. The search for other kinds of evidence failed to produce a smoking gun. First of all, there's no smoking gun. In the course of our investigation we did not find a single piece of evidence.
a smoking gun (or pistol)a piece of incontrovertible evidence.
This phrase draws on the assumption, a staple of detective fiction, that the person found with a recently fired gun must be the guilty party. The use of the phrase in the late 20th century was particularly associated with the Watergate scandal in the early 1970s involving the US President Richard Nixon . When one of the Watergate tapes revealed Nixon's wish to limit the FBI's role in the investigation, Barber B. Conable famously commented: ‘I guess we have found the smoking pistol, haven't we?’
1998 New Scientist This genetic smoking gun is evidence of a migration out of Asia that is hard to refute.
a/the ˌsmoking ˈgunsomething that seems to prove that somebody has done something wrong or illegal: This memo could be the smoking gun that investigators have been looking for.
n. the indisputable sign of guilt. The chief of staff decided that the admiral should be found with the smoking gun.
Definite evidence of illegal or criminal activity. The term alludes to smoke emitted by a revolver or other kind of gun that has been fired, but it is also used more broadly for other kinds of malfeasance. For example, Time (Sept. 19, 1977) had it, “In fact there may be no ‘smoking gun’—no incontrovertible black-and-white evidence of wrongdoing by Lance.” The New York Times (Oct. 3, 2004) quoted National Security Advisor Condoleezza Rice, talking on CNN about aluminum tubes in Iraq suspected to be used for nuclear weapons, “We don’t want the smoking gun to be a mushroom cloud.”