dead letter

American  

noun

1. a law, ordinance, etc., that has lost its force but has not been formally repealed or abolished.

2. a letter that cannot reach the addressee or be returned to the sender, usually because of incorrect address, and that is sent to and handled in a special division or department dead-letteroffice of a general post office.

---

dead letter British  

noun

1. a letter that cannot be delivered or returned because it lacks adequate directions

2. a law or ordinance that is no longer enforced but has not been formally repealed

3. informal anything considered no longer worthy of consideration

---

dead letter Idioms  

1. An unclaimed or undelivered letter that is eventually destroyed or returned to the sender. For example, She moved without leaving a forwarding address, so her mail ended up in the dead letter office . [c. 1700]

2. A statute or directive that is still valid but in practice is not enforced. For example, The blue laws here are a dead letter; all the stores open on Sundays and holidays . [Second half of 1600s]

---

Other Word Forms

• dead-letter adjective

Etymology

Origin of dead letter

First recorded in 1570–80

Example Sentences

Every day that passes makes that resolution more of a dead letter, and adds to the elusiveness of a deal.

From The Wall Street Journal • Oct. 23, 2025

This, Kagan says, renders impeachment and conviction virtually a dead letter.

From Salon • Nov. 18, 2024

If you don’t have effective enforcement, the law is a dead letter.

From Slate • Sep. 18, 2023

During the first week in January, when the next term opens, it will be a dead letter.

From Los Angeles Times • Oct. 30, 2022

Since the battalion had become so highly trained, Lord Clare's ingenious invention with respect to the testimony of a single witness was a dead letter.

From My Lords of Strogue Vol. III, (of III) A Chronicle of Ireland, from the Convention to the Union by Wingfield, Lewis