dead as a doornail

Dead, unresponsive, defunct. This simile dates from the fourteenth century and the source of it has been lost. A doornail was either a heavy-headed nail for studding an outer door or the knob on which a door knocker strikes. One plausible explanation for the analogy to death is that it alluded to costly metal nails (rather than cheap wooden pegs), which were clinched and hence “dead” (could not be re-used). The expression was used in a fourteenth-century poem of unknown authorship, William of Palerne, and was still current when Dickens wrote A Christmas Carol (1843). There have been numerous similar proverbial comparisons— dead as a mackerel, dead as mutton, dead as a herring, dead as a stone—but
this one, with its alliterative lilt, has survived longest.