A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage. They may also be used in industry to protect secret projects and the like from business rivals.

Proliferation of code names in World War II

In the Second World War, code names common to the Allies referring to nations, cities, geographical features, military units, military operations, diplomatic meetings, places, and individual persons were agreed upon adapting pre-war naming procedures in use by the governments concerned. In the British case code names were administered and controlled by ISSB (The Inter-Services Security Board) staffed by the War Office with the word list generated and randomised by GC&CS (later GCHQ). This procedure was coordinated with the USA when America entered the war. Random lists of code names were issued to users in alphabetical blocks of ten words and were selected as required. Code words became available for re-use after six months and unused allocations could be re-assigned at discretion and according to need. Capricious selection from the available allocation could result in clever meanings and result in an aptronym or backronym although policy was to select words that had no obviously deducible connection with what they were supposed to be concealing. Those for the major conference meetings had a partial naming sequence referring to devices or instruments which had an ordinal number as part of their meaning, eg the third meeting was "TRIDENT." The ruler of the Soviet Union, who had given himself the name "Stalin", meaning "man of steel," was given the code name "GLYPTIC," meaning "an image carved out of stone."

• Reference: Glossary of Code Names from U. S. Army in World War II - Washington Command Post: The Operations Division
• WWII Allied Operations
• Abbreviations, Acronyms, Codewords, Terms Appearing in WW II Histories and Documents
• Information from original files held at TNA:The National Archives formerly The Public Record Office which hold the publicly available records of central government for the UK

German code names

Ewen Montagu, a British Naval intelligence officer, discloses in Beyond Top Secret Ultra that during World War II, Nazi Germany habitually used ad hoc code names as nicknames which frequently openly revealed or strongly hinted at their content or function.

List of German code names:

• Golfplatz (German: Golfcourse) — Britain - employed by the Abwehr
• Samland — The United States (From Uncle Sam)- employed by the Abwehr
• Heimdall (A God whose power was "to see for a hundred miles") — long range radar.
• Wotan (one-eyed God) — Based on nothing more than this and the knowledge it was a radar system, R.V. Jones, a British scientist working for Air Intelligence of the British Air Ministry and SIS assumed that it used a single beam and from that determined the system it would have to use. His shrewd assessment was exactly correct. A counter-system was quickly created which made Wotan useless.
• Operation Seelöwe (Sealion) — Plans to invade Britain (The Royal Coat of Arms of England depicting three lions passant guardant).
• Operation Barbarossa (Frederick Barbarossa) — Plans to go east and invade the Soviet Union.