"(as|) dead as a (doornail|herring)" 的定义和意义

What is the origin of the idiom "dead as a doornail" and when to use it?

The idiom "dead as a doornail" has uncertain origins but has been in use since at least the 14th century. This phrase was likely popularized by Charles Dickens in "A Christmas Carol." It is now used to imply that something is commonly used to describe something that is completely lifeless or inanimate, with no possibility of revival or recovery. It is often applied to objects, ideas, or situations rather than living creatures.