幼 is a bound morpheme (b.f.) meaning 'young, small, immature'. It cannot stand alone as a word; instead, it appears as a prefix or root in compounds such as 幼儿 (young child), 幼稚 (naive), 幼苗 (seedling), and 幼虫 (larva). Learners should think of it as a building block for vocabulary related to youth and early stages, not as a free-standing adjective like 小.