infantilism

noun

1. the persistence in an adult of markedly childish anatomical, physiological, or psychological characteristics.
2. an infantile act, trait, etc., especially in an adult.
3. a speech disorder characterized by speech and voice patterns that are typical of very young children.

noun

1. psychol
   1. a condition in which an older child or adult is mentally or physically undeveloped
   2. isolated instances of infantile behaviour in mature persons
2. childish speech; baby talk

n.

1. A state of arrested development in an adult, characterized by retention of infantile mentality, accompanied by stunted growth and sexual immaturity, and often by dwarfism.
2. Extreme immaturity, as in behavior or character.