Origin of dead-as-a-doornail
One of the earliest usages in English is in William Langland's poem Piers Plowman A. i. 161 "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 Parliament of the Three 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.