secret language (?.)

• Aesopian language
• Babel
• Greek
• argot
• babble
• cant
• cipher
• code
• coded message
• cryptoanalysis
• cryptoanalytics
• cryptogram
• cryptograph
• cryptographer
• cryptography
• double Dutch
• garble
• gibberish
• gift of tongues
• glossolalia
• gobbledygook
• invisible ink
• jargon
• jumble
• noise
• scramble
• secret writing
• slang
• sympathetic ink