| Subject | English | Russian |
| astronaut. | code letter | кодовая буква |
| IT | code letter | условная буква |
| gen. | coded letter | зашифрованное письмо (также "шифрованное письмо" • A coded letter penned by the King of Spain in the 16th century has been deciphered by a team of researchers.  coasttocoastam.com ART Vancouver) |
| tech. | letter code | буквенный код |
| telecom. | letter code | алфавитный код |
| tech. | letter code | код литеры |
| tech. | letter code | код буквы |
| gen. | letter-coded file | литерное дело (A registry file in KGB intelligence agencies containing materials relating to counter-intelligence work, or to diplomatic, trade and other missions and Soviet establishments abroad, or scientific and other delegations traveling abroad (from google.com Tanya Gesse) |
| gen. | work out a coded letter | расшифровать зашифрованное письмо |