Dead as a doornail is a common idiom, but what exactly is a doornail, and why is it dead? The saying goes at least as far back as the 1350’s, and may simply refer to the fact that the nails used to make big, heavy doors were securely fixed in place – the modifier dead having the same sort of unequivocal sense suggested in the expression “dead certain.” This is part of a complete episode.

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