noun

a system of words, letters, figures, or symbols used to represent others, especially for the purposes of secrecy.

the Americans cracked their diplomatic code

cipher,secret language,secret writing,set of symbols,key,hieroglyphics,coded message,cryptogram,cryptograph

verb

convert (the words of a message) into a code so as to convey a secret meaning.

only Mitch knew how to read the message—even the name was coded