The story
From Ancient Greek κρυπτός (kruptós, “hidden”) + -φασία (-phasía, “speech”) (from φάσις (phásis, “utterance”), from φημί (phēmí, “I speak”)). Equivalent to crypto- + -phasia.
Etymology from Wiktionary, CC BY-SA 4.0.
cryptophasia
Today it means: The development by twins (identical or fraternal) of a language that only they can understand. Full definition →