2、puerile:  Latin puer denoted ‘child’, or more specifically ‘boy’ (like Greek pais ‘child’, source of English paediatric, pedagogue, etc, it came ultimately from a base which signified ‘smallness’, and also gave English pusillanimous). The derived adjective puerīlis ‘childlike’ began to acquire its negative connotations in Latin, and brought them with it into English. The related puerperal ‘of childbirth’  comes from a Latin compound formed from puer and parere ‘give birth’ (source of English parent).=> pusillanimous
4、1660s, "youthful, boyish," a back-formation from puerility, or else from French puéril (15c.), from Latin puerilis "boyish; childish," from puer "boy, child" (see puerility). Disparaging sense, "juvenile, immature," is from 1680s.