In cryptography a nomenclator is a system of encryption that relies on a cipher alphabet and a lexicon of codewords. The codewords are substituted for their counterparts of the plaintext. And the rest of the message is encrypted using the cipher alphabet.

No"men*cla`tor (?), n. [L., fr. nomen name + calare to call. See Name, and Calendar.]

1.

One who calls persons or things by their names.

⇒ In Rome, candidates for office were attended each by a nomenclator, who informed the candidate of the names of the persons whom they met and whose votes it was desirable to solicit.

2.

One who gives names to things, or who settles and adjusts the nomenclature of any art or science; also, a list or vocabulary of technical names.

© Webster 1913.