as dead as a doornail

Related to as dead as a doornail: at one fell swoop

(as) dead as a doornail

1. Definitively dead. (Doornails were hammered in a such a way that they could not be reused.) I poked that squirrel with a stick and, yeah, it's as dead as a doornail.
2. Totally defunct. That idea from last week's meeting is dead as a doornail now that the CEO has vetoed it.
See also: dead, doornail
Farlex Dictionary of Idioms.

as dead as a doornail

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.
See also: dead, doornail
Endangered Phrases by Steven D. Price
See also:
  • (as) dead as a doornail
  • dead as a doornail
  • doornail
  • herring
  • (as) dead as a herring
  • (as) dead as mutton
  • mutton
  • dead as mutton
  • be dead in the water
  • dead in the water