A name used so that someone’s or something’s real name stays secret. Spies, police, army plans, and new products all use them. It might be a single odd word, or something like “Operation…” The point is hiding identity on purpose, not making a cute nickname for friends. You will see it written code-name, code name, or codename — all three appear. Though actually, once the secret is out, people often keep the code-name anyway, because that is the name that became famous. It can name a person, a plan, or a thing still being built.

代號