公式
こうしき · koushiki · JLPT N2 · na-adj
official
🧪 公 (public) + 式 (form/style): a public, set form, like a chemist's formula
Compound 公式 = 公 (public, official) + 式 (style, form). Hence formula, a set form, and formality. Use 'koushiki' as 'ko-SHI-ki': say 'cos-sh-key' to recall it.
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.'
式 — 工 (work) + 弋 (phonetic)
式 is a phono-semantic compound: 工 ('work, craft') gives the meaning of a tool, rule, or method, while 弋 supplies the sound. It originally referred to a standard pattern or model used in craftsmanship, then broadened to mean 'style, form, ceremony, or formula.'