
1) Address ender 2) Address ending 3) Address must 4) Address part 5) Daily sorting criterion 6) Delivery aid 7) Letter digits 8) Mail expediter 9) Mail must 10) Mail system 11) Number on a letter 12) Number to remember 13) Numbers on a letter 14) Numbers on letters 15) Part of a mailing address 16) Quint-essential number
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https://www.crosswordclues.com/clue/zip-code

A geographical classification system developed by the U.S. government for mail distribution, a nested numeric range of 5 to 9 numbers.
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http://archive.ifla.org/VII/s34/pubs/glossary.htm

ZIP codes are a system of postal codes used by the United States Postal Service (USPS) since 1963. The term ZIP, an acronym for Zone Improvement Plan, is properly written in capital letters and was chosen to suggest that the mail travels more efficiently, and therefore more quickly (zipping along), when senders use the code in the postal address. ...
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http://en.wikipedia.org/wiki/ZIP_code

system of zone coding introduced by the U.S. Post Office Department (now the U.S. Postal Service) in 1963 to facilitate the sorting and delivery of ... [1 related articles]
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http://www.britannica.com/eb/a-z/z/9

Registered trademark of the Postal Service; a five- or nine-digit code identifying locations in the United States.
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http://www.nmoa.org/Library/index.htm

[
n] - a code of letters and digits added to a postal address to aid in the sorting of mail
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http://www.webdictionary.co.uk/definition.php?query=zip%20code
ZIP noun a code of letters and digits added to a postal address to aid in the sorting of mail
Found on
https://www.encyclo.co.uk/local/20974

a system used in the U.S. to facilitate the delivery of mail, consisting of a five- or nine-digit code printed directly after the address, the first five digitsindicating the state and post office or postal zone, the last fourthe box section or number, portion of a rural route, building, or other specific delivery location.
Found on
https://www.infoplease.com/dictionary/zip-code
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