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Longman Dictionary of Contemporary English
code name
noun
EXAMPLES FROM CORPUS
▪ Fascination with code names went well beyond operations, reaching even the contra supporters and fund-raisers.
▪ He decided to give the various systems code names based on the colors of the spectrum.
▪ It was preceded by a scrupulous recce weeks before in a restaurant near his house with the code name Pomme d'Amour.
▪ Medusa was the code name of a back-up disk suite product brought to market a year ago.
▪ The new system was as deep and mysterious as its chromatic code name implied.
▪ The Triumph code name, by the way, has been changed.
Wiktionary
code name

n. (context business espionage military English) A name used to clandestinely identify somebody or something, either for military or espionage purposes, or for commercial confidentiality.

Wikipedia
Code name

A ' code name' or cryptonym is a word or name used, sometimes clandestinely, to refer to another name, word, project or person. Names are often used for military purposes, or in espionage. They may also be used in industrial counter- industrial espionage to protect secret projects and the like from business rivals, or to give names to projects whose marketing name has not yet been determined. Another reason for the use of names and phrases in the military is that they transmit with a lower level of cumulative errors over a walkie-talkie or radio link than actual names.

Usage examples of "code name".

Captain Prince Lysander, code name Kicker Six, who would be leading the scout element.

Her staff found her code name ironic for several reasons, but mostly because she was not in the least charming.

And now she knew for sure the code name Starscream was a password into secret files inside the Infirmary.