Dead as a Doornail: Origin and Meaning
Back in the 14th century, front doors were built using heavy hand-forged nails to strengthen the vertical and horizontal panels of a door or as decorations.
Once the nails were placed into position their protruding heads were hammered down and over into the wood to secure them, making them unusable if ever removed. The bent nails were commonly called “dead”, hence the expression dead as a doornail.
– I poked the fox I found in the garden with a stick, but, alas, it was as dead as a doornail.
– The negotiations reached a stalemate. I think the deal is as dead as a doornail.