The phrase 'Stone Dead' means dead; unquestionably dead; long dead.
Example of Use: "The cat was stone dead and stiff as a board by the time we got to him."
Interesting fact about Stone Dead
Scholars are not certain about the origin of the idiom 'stone dead' but it is a term that is quite easy to understand. The saying is believed to be a variation on a 1350 idiom: 'dead as a doornail.' About the same time, people used idioms such as 'dead as mutton,' 'dead as herring,' and 'dead as a stone.'
