doornail

To be unable to hear well or at all. I hope grandpa wears his hearing aid to dinner tonight because he's as deaf as a post without it. After years of listening to loud rock music, I'm deaf as a post.

dead; no longer in existence. (*Also: as ~.) That silly old idea is dead as a dodo. When I tried to start my car this morning, I discovered that the battery was deader than a doornail.

to be dead I found the fish, dead as a doornail, floating on the surface of the water. At first I though Jake was dead as a doornail, but he was only fast asleep.

to be completely deaf She's 89 and as deaf as a post.

Also, dead as a dodo or herring . Totally or assuredly dead; also finished. For example, The cop announced that the body in the dumpster was dead as a doornail, or The radicalism she professed in her adolescence is now dead as a dodo, or The Equal Rights Amendment appears to be dead as a herring. The first, oldest, and most common of these similes, all of which can be applied literally to persons or, more often today, to issues, involves doornail, dating from about 1350. Its meaning is disputed but most likely it referred to the costly metal nails hammered into the outer doors of the wealthy (most people used the much cheaper wooden pegs), which were clinched on the inside of the door and therefore were "dead," that is, could not be used again. Dead as a herring dates from the 16th century and no doubt alludes to the bad smell this dead fish gives off, making its death quite obvious. Dead as a dodo, referring to the extinct bird, dates from the early 1900s.

Undoubtedly dead.

Really dead. Doornails, which provided strength and decoration, were hammered into the wood and then clenched for additional grip. Because a doornail was bent, it could not be used again, which made it even deader. A more recent phrase is “as dead as last year's tennis balls.” In the era before year-round indoor tennis, they would have lost their bounce before the start of the next season.