1 . A pronunciation disorder in which the child uses speech sounds that are meaningless, below the level for his or her age. 2 . It is said of a language invented and spoken by one or very few people. Most of the time, idioglossia refers to the "private tongues" of young children, especially twin siblings. It comes from the Greek idios, 'proper', 'particular'; the Greek glôssa, 'tongue'; and the Greek -ia, 'quality'.