効率
こうりつ · kouritsu · JLPT N1 · noun
efficiency
⚙️ 効 (effect) + 率 (rate) = effect per unit of input, i.e. efficiency
効 means effect or result, and 率 means rate or ratio. Together they name the ratio of useful output to input, which is efficiency.
率 — twisted silk threads with droplets, plus 十
率 originally pictured a net or twisted bundle of silk cords with water droplets shaking off, suggesting something being led or pulled along. From 'leading a rope' it extended to 'lead, command' (shuài) and to 'rate, ratio' (lǜ), as in a fixed proportion. The two readings share this core image of a guiding measure.