dead letter

• Закон, правило или соглашение, которое официально остается в силе, но больше не применяется и не соблюдается; также относится к письму, которое не может быть доставлено почтовой службой из-за неправильного или отсутствующего адреса.

A law, rule, or agreement that remains officially in effect but is no longer enforced or followed; also refers to a letter that cannot be delivered by the postal service due to an incorrect or missing address.

1. Unenforced law or ruleC1formal

   A law, regulation, or agreement that remains officially in effect but is no longer applied or enforced.

   Мёртвая буква

   • The old prohibition law is now a dead letter.
   • Many outdated regulations have become dead letters in modern society.
   • The treaty was signed but quickly became a dead letter.

2. Undeliverable mailB2formal

   A piece of mail that cannot be delivered to the intended recipient or returned to the sender.

   Недоставленное письмо

   • The post office has a special department for handling dead letters.
   • This letter was returned as a dead letter because the address was wrong.
   • Dead letters are eventually destroyed if unclaimed.