- immature or childish behavior
- Psychol. any abnormal state in which childish behavior or childlike traits persist into adult life: marked by intellectual disability and stunted growth and by failure to mature sexually
- 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.
- a. Marked immaturity, as in behavior or character: “infantilism, which is the subtext of so much American cinema and culture” (John Simon).b. An infantile act or remark.