原子序数 yuánzǐxùshù atomic number Origin Definitions Defs Strokes Stroke Words Sentences Sents 原子 yuánzǐ noun atom atom; atomic; the smallest unit of a chemical element, consisting of a nucleus surrounded by electrons序数 序數 xùshù ordinal number ordinal number; any number used to show the order or sequence of things. In Chinese, these are often formed by adding 第 dì before a number.