smoking gun

noun

1. indisputable proof or evidence of a crime.

smoking gun

noun

1. a piece of irrefutable incriminating evidence

Word History and Origins

Origin of smoking gun¹

First recorded in 1970–75

Idioms and Phrases

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]