by Caleb Reynolds
Such an odd phrase, “dead as a door nail.” It is one of those phrases that has been around so long that we hardly ever think about using it, even long after our doors no longer have nails in them. I place it in the same family as “to film someone,” “blow off steam,” “been through the wringer,” and “dial the phone”; phrases that are ingrained in the English language so deep that we continue to use them long after their meanings are forgotten.
“Dead as a door nail” has been around a long time, since the days of the beginning of the English language. The oldest known written account is from the 14th century poem “The Romance of William of Palerne,” which is a translation of a 13th century Flemish poem called “Guillaume de Palerne.”
hurth the bold bodi he bar him to the erthe,
as ded as dornayl te deme the sothe. 
The anonymous 14th century poem “The Parliament of the Three Ages” contains “There he was crepyde into a krage and crouschede to the erthe. / Dede als a dore-nayle doun was he fallen.”  In William Langland’s Piers Plowman, [1370-90] we find the phrase “Fey withouten fait is febelore then nought, And ded as a dore-nayl”.
William Shakespeare used it twice in “Henry IV part 2”:
Act V, Scene 3:
“Falstaff: What! is the old king dead?
Pistol: As a nail in a door.”
and again in Act IV, Scene 10:
Cade: Brave thee! ay, by the best blood that ever was
broached, and beard thee too. 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.
The “Oxford English Dictionary” gives the following:
Door-nail: A large-headed nail, with which doors were formerly studded for strength, protection, or ornamentation: now chiefly in the alliterative phr. as dead, deaf, dumb, dour, as a door-nail: see DEAD a. 32b., DEAF a. 1d., etc. (Conjectured by Todd to be “The nail on which in ancient doors the knocker struck.” No evidence of this appears.)
c1350 [see DEAD a. 32b]. 1350 in Riley Lond. Mem. (1868) 262, 3000 dornail..7200 dornail. a1400-50 Alexander 4747 Dom as a dore-nayle & defe was he bathe. 1593-1680 [see DEAD 32b.]. 1854 MRS. GASKELL North & S. xvii, Thornton is as dour as a doornail. 1866 ROGERS Agric. & Prices I. 497 Door-nails, floor and roof-nails.
dead a., entry 32b. dead as a door-nail, dead as a herring: completely or certainly dead. Also, (as) dead as the (or a) dodo, (as) dead as mutton.
c1350 Will. Palerne 628 For but ich haue bote of mi bale I am ded as dorenail. 1362 LANGL. P. Pl. A. I. 161 Fey withouten fait is febelore en nout, And ded as a dore- nayl. 1593 SHAKES. 2 Hen. VI, IV. x. 42 If I doe not leaue you all as dead as a doore naile. [1598 SHAKES. Merry W. II. iii. 12 By gar, de herring is no dead, so as I vill kill him.] 1664 BUTLER Hud. II. iii. 1148 Hudibras, to all appearing, Believ’d him to be dead as Herring. 1680 OTWAY Caius Marius 57 As dead as a Herring, Stock-fish, or Door- nail. 1792 I. BICKERSTAFFE Spoil’d Child II. ii. 32 Thus let me seize my tender bit of lambthere I think I had her as dead as mutton. 1838 [see MUTTON 7]. 1856 READE Never too late lx, Ugh! what, is he, is he Dead as a herring. 1884 Pall Mall G. 29 May 5/2 The Congo treaty may now be regarded as being as dead as a doornail. 1904 H. O. STURGIS Belchamber iv. 51 The Radicalism of Mill..is as dead as the dodo. 1919 W. S. MAUGHAM Moon & Sixpence ii. 10 Mr. Crabbe was as dead as mutton, but Mr. Crabbe continued to write moral stories in rhymed couplets. 1935 Ann. Reg. 1934 II. 305 References appearing in the London newspapers to the effect that “war debts are as dead as the Dodo” were cabled to the American press. 1960 Guardian 24 Mar. 11/1 Mr. Menzies..refused a request for a boycott..saying he had hoped this “was as dead as a dodo.”
But, what does it mean? I do not know, but there are some theories.
The first among them is that the phrase refers to the method of attaching hinges to doors. The hinges were mounted on the outside of the door via straps and the nails were hammered into the door, through the straps, from the outside, and then bent around and driven back into the door from the inside, driving the life from the nails so that they could never be used again.
While that makes it almost impossible to pull the nails out of the door from the outside, I do not buy the idea that the nails could never be straightened out, once removed, and used again. They were iron; they could be heated and pounded straight. But, I will concede that for the average person (i.e., not a blacksmith) once you remove a bent-over door nail, it was useless as a nail. But, how often were doors taken apart?
The second theory is that the door nail was the nail hammered into the door on which the door knocker would hit. Some sources indicate that after years of being hit, the door nail would loosen and fall out of the door. Apparently, when the nail hit the ground, it would make a “tink” sound instead of ringing like a new nail; thus, the door nail was dead. I don’t like this idea either. If a knocker is pounding a nail into a door, it is not very likely to fall out of the door on the side to which it is being struck. Plus, I’ve visited houses and churches which have stood for a few hundred years that still have functioning door knockers. If a door knocker and strike nail can withstand a couple of centuries of abuse, I think that it is not very likely that the strike nail would fall out and “die” often enough for the phrase to enter the English language.
Another theory related to the door knocker is that the strike nail was hit on the head in the way royalty was struck on their heads to ensure that they were truly dead and not just sleeping. A: I cannot find any period confirmation of this practice. and B: it’s stupid. “I’m sorry for hitting you in the head with a hammer, Your Majesty. I wanted to see if you were dead or just napping.” Thank you, Internet.
My thought is that the strike nail, when hit by the door knocker, sounds dead. Not a high pitch “ting” that one would get if you drop a nail on a flagstone, but a “thunk” noise that might sound more like a coffin being nailed shut then if you hit two pieces of metal together.
We might never know the true meaning of the phrase, but, since English is the pack-rat of languages, I predict that “dead as a door nail” will be used far into the future when everyone will have Star Trek-style automatic, sliding doors.
 “and bears him down to the earth, as dead as a door nail.”
 “He had crept into a cave and crouched to the earth / Dead as a door-nail down he had fallen.”
 You are on your own with this one.
Hulme, Frederick Edward. “Proverb Lore: Many Sayings, Wise Or Otherwise, on Many Subjects, Gleaned from Many Sources.” Elliot Stock, 1902
Langland, William; Economou, George. “William Langland’s Piers Plowman: The C Version : a Verse Translation.” University of Pennsylvania Press, 1996
“The Oxford English Dictionary.” Oxford University Press
“The Romance of William of Palerne: (otherwise Known as the Romance of “William and the Werwolf”) Translated from the French at the Command of Sir Humphrey de Bohun, about A.D. 1350; to which is Added a Fragment of the Alliterative Romance of Alisaunder; Translated from the Latin by the Same Author, about A.D. 1340.” Early English text society, 1867
Shakespeare, William. “The Second part of King Henry the Fourth.” The Complete Works of William Shakespeare. The Tech, MIT
Skeat, Walter W. ed. “The romance of William of Palerne: (otherwise known as the romance of “William and the werwolf”)” London, Pub. for the Early English Text Society, by N. Trubner & Co. 1867