From Longman Dictionary of Contemporary English(as) dead as a doornail(as) dead as a doornailinformal completely dead → doornail
Examples from the Corpus
(as) dead as a doornail• She looked dead as a doornail.• If looks could kill, Dooley Barlowe would have dropped him right there, dead as a doornail.• There we were, messing around with his things, and all the time he was dead as a doornail in Paris. 