- a law, practice, etc. no longer enforced or operative but not formally done away with
- a letter that cannot be delivered or returned, as because of incorrect address and lack of return address
See dead letter in American Heritage Dictionary 4
- An unclaimed or undelivered letter that after a period of time is destroyed or returned to the sender by the postal service.
- A law, directive, or factor still formally in effect but no longer valid or enforced.
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