smoking gun

A smoking gun is a clear piece of evidence. A babysitter who's trying to figure out which kid ate the last chocolate cupcake might consider one child's frosting-smeared face to be a smoking gun.

Evidence that's so strong it seems undeniable is a smoking gun, whether it's a shredded piece of math homework in your dog's mouth or a clear fingerprint on a stolen diamond ring. A smoking gun almost always proves clearly that a particular person is guilty of something. It comes from the idea that a recently fired gun — still smoking — in a suspect's hand proves his guilt, and it was first used in the 1970's.

Definitions of smoking gun
  1. noun
    indisputable evidence (especially of a crime)
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    type of:
    evidence
    an indication that makes something evident
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