dead as a doornail

Etymology
From. One of the earliest usages in English is in William Langland's poem Piers Plowman A. i. 161 (late 14th century) "Fey withouten fait is febelore þen nouȝt, And ded as a dore-nayl", though it is unlikely this is Langland's invention. It also appears in the English William of Palerne l. 628 "For but ich haue bote of mi bale‥I am ded as dore-nail" and in the alliterative debate poem The Parlement of the Thre Ages "Dede als a dore-nayle doune was he fallen" 65. Both of these texts are of uncertain date, and may predate Langland's usage.

One plausible explanation is that doors were built using only wood boards and hand-forged nails: the nails were long enough to dead nail the (vertical) wooden panels and (horizontal) stretcher boards securely together, so they would not easily pull apart. This was done by pounding the protruding point of the nail over and down into the wood. A nail that was bent in this fashion (and thus not easily pulled out) was said to be "dead", thus dead as a doornail.

Adjective

 * 1)  Unquestionably dead. Used for both inanimate objects and once living beings.
 * 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.
 * 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.
 * 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.
 * 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.
 * 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.

Translations

 * Arabic: شبع موت
 * Danish: død som en sild, stendød
 * Finnish: kuollut kuin kivi
 * French: mort et bien mort
 * German:
 * Icelandic: steindauður
 * Norwegian:
 * Bokmål:
 * Polish: zimny trup
 * Russian:, абсолю́тно мёртвый