dead as a doorknob
Possibly from a misinterpretation or misunderstanding of the expression dead as a doornail. See usage notes below.
- (simile) Entirely, unquestionably or certainly dead.
- I tried the flashlight, but the battery was as dead as a doorknob.
- I found the mouse who lived in our wall, lying on his back with his feet in the air—as dead as a doorknob.
Many other nouns can be substituted for "doorknob", perhaps the oldest being "doornail" used by William Shakespeare, in Henry VI, Part 2, act 4, scene 10, and also in A Christmas Carol. Other common forms include doormat, dodo, rock, graveyard.