"Su", a commonly used Chinese word (first-class word), pronounced "Si", was first seen in Oracle Bone Inscriptions in Shang Dynasty. The original meaning is the name of the plant, millet, with round or oval fruit. It is commonly known as "millet" in the north, and it is called "millet" after peeling. In ancient Chinese, all common crops and grains can generally be used as the general name of grains or grains, and "millet" actually has this function; The grain of "millet" is very small, so it is used to refer to tiny things; "Su" is also the name of ancient units of measurement; Because "millet" can be used as a container or as a general term for grain, the salary received by ancient officials is grain, so "millet" can also be extended to mean salary.