The codename was used to protect classified information.
secret mission
Frequency:
55
%
The codename was used for the secret mission.
covert operation
Frequency:
50
%
The codename was assigned to the covert operation.
undercover agent
Frequency:
45
%
The codename was given to the undercover agent.
Idiomatic Expressions for codename
Phrase: reveal one's codename
Meaning: to disclose or make known one's secret or false name
Usage: The undercover agent accidentally revealed his codename to the enemy.