A coffin is a box in which a dead body is buried or cremated.
PHRASE
促使…失敗（或完結）的因素
If you say that one thing is a nail in the coffin of another thing, you mean that it will help bring about its end or failure.
例句
A fine would be the final nail in the coffin of the airline.罰款將會是對這家航空公司的最后致命一擊。
英漢詞典釋義
n.
棺材
The coffin lid had been screwed down.棺材蓋已經蓋緊了。The sight of the coffin sent a shudder through him.看到那副棺材，他渾身一陣戰栗。They bore the coffin into the church.他們把棺材抬進教堂。The coffin was placed in the grave.那口棺材已安放到墳墓里去了。
使某人早亡〔死,完蛋,垮臺等〕之物
I missed the deadline again last week; I suppose that is another nail in my coffin.上星期我又誤了最后期限,我想那是另一個促使我完蛋的錯誤。