公函
gōng hán · HSK 7
official letter
📜 公 = public/official + 函 = letter/correspondence
公 means public or official (think 公司 company, 公园 park). 函 means letter or correspondence, as in 信函. Together 公函 is an official letter sent between organizations or government bodies.
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.'