Question

Where does the expression "dead as a doornail" come from?

Answer 1

The expression seems to be in use since the 1300s.

Explanation:

A English print of the translated French poem Guillaume de Palerne (translated by William Langland) was seen in 1350.

The expression became more common and was used by Shakespeare in his play King Henry VI :
'Look on me well: I have eat no meat these five days; yet, come thou and thy five men, and if I do not leave you all as dead as a doornail, I pray God I may never eat grass more.'

Later, Dickens used it in his famous work, A Christmas Carol :
'You will therefore permit me to repeat, emphatically, that Marley was as dead as a door-nail.'

Reference: http://www.phrases.org.uk/meanings/as-dead-as-a-doornail.html