noun
secret name; code name
Refers to a name used to conceal someone's true identity, often in espionage, military, or organizational contexts.
スパイは任務中、秘匿名を使っていた。
The spy used a code name during the mission.
コードネーム is a direct loanword for 'code name', more common in modern contexts; 秘匿名 is a native Japanese compound with a similar meaning but may sound more formal or literary.
Compound of 秘 (secret) + 匿 (hide) + 名 (name). The exact historical derivation is uncertain, but the kanji combination transparently conveys the meaning of a concealed name.