1 general:: Phrase(s): *dead as a dodo [and] *dead as a doornail; deader than a doornail 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.
McGrawhill's American Idioms And Phrasal Verbs