公斤
gōngjīn · HSK 2
kilogram
⚖️ 公斤 = 公 (public/standard) + 斤 (catty/weight) = kilogram
斤 is the traditional Chinese unit of weight (~500g); prefixing 公 (public/metric) marks it as the international standard unit — the kilogram. Same pattern as 公里 (kilometer) and 公分 (centimeter).
公 — eight 八 + private 厶
Originally an ideograph showing 八 (to divide) over 厶 (private/self), depicting the act of splitting away from selfish interest. The combination came to mean 'public' or 'fair,' the opposite of private. It later extended to senses like 'duke,' 'lord,' and 'grandfather.'
斤 — axe pictograph 斤
斤 is a pictograph of an ancient axe or adze, with the curved top showing the blade and the lower stroke the handle. From 'axe' it came to mean the chopping it does, and was later borrowed as a unit of weight (catty, ~500g), its modern everyday sense.