The word **指甲油** (zhǐjia yóu), meaning "nail polish," is a straightforward compound noun formed by combining three meaningful characters: **指** (zhǐ, finger), **甲** (jiǎ, armor/shell, here meaning "nail"), which together create **指甲** (zhǐjia, fingernail or toenail), and **油** (yóu, oil or paint). The term is constructed logically through modification, where "nail" (指甲) is modified by "oil/paint" (油) to specify the type of cosmetic product, resulting in a clear, descriptive term for the substance applied to nails.