"Designating the later stages of an animal's growth, in which it acquires adult characteristics", Late 19th cent.; earliest use found in Sydney Buckman (1860–1929), geologist and palaeontologist. From ancient Greek νεανικός youthful from νεανίας young man (from νέος new, young + an element or elements of disputed origin) + -ικός.[neanic etymology, neanic origin, 英语词源]