As dead as a doornail
Dead, devoid of life (when applied to people, plants or animals). Finished with, unusable (when applied to inanimate objects).
This is old - at least 14th century. There's a reference to it in print in 1350, a translation by William Langland of the French poem Guillaume de Palerne:
"For but ich haue bote of mi bale I am ded as dorenayl."
Langland also used the expression in the much more famous poem The Vision of William Concerning Piers Plowman, circa 1362:
Fey withouten fait is febelore þen nouȝt, And ded as a dore-nayl.
[Faith without works is feebler than nothing, and dead as a doornail.]
The expression was in widespread colloquial use in England by the 16th century, when Shakespeare gave these lines to the rebel leader Jack Cade in King Henry VI, Part 2, 1592:
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.
There are several 'as dead as...' idioms, amongst the most notable examples being 'as dead as a dodo' and 'as dead as mutton'. Dodos and mutton are unquestionably dead, but why doornails are cited as a particular example of deadness isn't so obvious.
Doornails are the large-headed studs that were used in earlier times for strength and more recently as decoration. The practice was to hammer the nail through and then bend the protruding end over to secure it. This process, similar to riveting, was called clenching. This may be the source of the 'deadness', as such a nail would be unusable afterwards.
Dickens was among the celebrated authors who liked the phrase and made a point of musing on it in A Christmas Carol
Old Marley was as dead as a door-nail.
Mind! I don’t mean to say that I know, of my own knowledge, what there is particularly dead about a door-nail. I might have been inclined, myself, to regard a coffin-nail as the deadest piece of ironmongery in the trade. But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country’s done for. You will therefore permit me to repeat, emphatically, that Marley was as dead as a door-nail.
Doornails have been top of the 'as dead as' pops since the 1300s. Perhaps it's time for a 21st century upgrade? Given the ubiquity of digital downloads, I'll put in an early bid for 'as dead as a DVD'.
See other 'as x as y similes'.
See other phrases and sayings from Shakespeare.