Real Dictionary

code word
countable noun: A code word is a word or phrase that has a special meaning, different from its normal meaning, for the people who have agreed to use it in this way.

code word in American English
a word or phrase with a secret meaning, often, specif., one used to convey an idea or attitude that cannot be openly divulged because it is socially or politically unacceptable
noun

code word in British English
noun: a word used to identify a classified plan, operation, etc