The Chinese word 孩子气 (háiziqì) is a compound adjective formed through a common grammatical construction where the noun 孩子 (háizi), meaning "child," is combined with the nominal suffix 气 (qì), which in this context means "air," "manner," or "temperament." Literally, it translates to "child-air," but it functions idiomatically to describe an adult's behavior or personality that resembles that of a child, carrying the meaning of "childish" or "juvenile." The formation follows a pattern similar to other descriptive terms like 书生气 (shūshēngqì, "bookish") or 江湖气 (jiānghúqì, "having a roguish or adventurer's spirit"), where 气 abstracts and characterizes the essential quality of the preceding noun.