能率
のうりつ · nouritsu · JLPT N2 · noun
efficiency
🔋 能 = energy/ability + 率 = rate: how much energy turns into work = efficiency
能 means energy or ability and 率 means ratio or rate. Together they measure how much useful output you get from a given input, which is efficiency.
能 — 厶 (head) + 月 (body/flesh) + 匕匕 (legs)
Originally a pictograph of a bear, showing its head, body, and powerful legs. Because bears were seen as strong and capable, the character was borrowed to mean 'ability' or 'can'. A new character 熊 (with the fire radical 灬) was later created for 'bear'.
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.