IPA: /ɪnˈfæntɪlɪzəm/
KK: /ɪnˈfæntɪlɪzəm/
A condition where an adult shows immature behavior or characteristics, often keeping traits typical of a child, such as emotional or mental qualities that are not fully developed.
His tendency to throw tantrums and avoid responsibilities is a clear sign of infantilism.
Infantilism → It is formed from "infans" (from Latin, meaning infant or child) and "-ism" (meaning a practice or philosophy). The word refers to a condition or practice characterized by childlike behavior or attitudes.
Think of 'infans' which means infant, and remember that 'infantilism' describes a practice or condition of behaving like a child.