The word 公斤 is formed by combining two characters: 公 (gōng), meaning "public" or "common", and 斤 (jīn), which is a traditional Chinese unit of weight (approximately 500 grams). Together, they create a compound word where 公 acts as a modifier, indicating that this is the "common" or "standard" (i.e., metric) version of the "斤". Thus, 公斤 literally means "common jin" and was adopted to represent the kilogram when the metric system was introduced, distinguishing it from the traditional Chinese unit.