What is another word for dead letter?
Pronunciation: [dˈɛd lˈɛtə] (IPA) 
Dead letter is an idiomatic expression used to describe an unclaimed, undeliverable, or unreadable letter. The phrase can also be used in the context of a law or business that is no longer enforced or effective. There are other phrases and terms that are synonymous with dead letter, such as "letter of a bygone era," "null and void," "obsolete," "archaic," "inactive," and "outdated." Each of these words describes something that has lost its relevance or usefulness, like an old-fashioned letter or a law that no longer serves its intended purpose. Whatever the term used to describe it, a dead letter signifies a message or rule that has been rendered obsolete by time or circumstances.
