smoking gun的意思是鐵證如山，確鑿證據。比如：So far，we haven't found a smoking gun to prove he committed the crime.目前為止，我們還沒找到確鑿證據證明他犯罪。
這是近年來才出現的用語，據說起源於20世紀70年代。其概念非常簡單：如果-把槍剛剛擊發的話，因為槍枝內部發生爆炸，所以槍管一定會冒煙。因此如果某人被逮到時，手上正好拿著一把冒煙的槍，則此人必定是罪犯。這個用語其實與前美國總統尼克森有段有趣的淵源，有名政客聽到尼克森的水門事件錄音帶，將這卷錄音帶稱之為smoking gun，因此有些資料顯示這名政客就是創造這個用語的人。
看看老外聊天時怎麼用smoking gun:
Gertrude：I know my husband is cheating on me.
我知道我先生對我不忠。
Earl：What was the smoking gun？
有什麼確切證據嗎？
Gertrude：I saw a romantic text message he got from another woman.
我看到其他女人傳給他的曖昧簡訊。
Earl：It seems like that's pretty strong proof.
這似乎是非常有力的證據。
smoking gun例句精選：
But we still haven't found the smoking gun.
但是我們還沒有找到確鑿的證據。
The smoking gun was the lipstick on his collar.
他衣領上的口紅是確鑿的證據。
The tape recordings provided prosecutors with the smoking gun they needed to prove he'd been involved in the conspiracy.
錄音磁帶為檢察官們提供了所需的確鑿證據，證明了他與陰謀活動有關。
Police are still looking for a smoking gun in the kidnapping case.
警察仍然在尋找綁架案的有力證據。