长效
cháng xiào · HSK 7
to be effective over an extended period
🔋⏳ long + effect = lasting effectiveness
长 means long and 效 means effect or result. Together they describe something that keeps working over a long span — like a slow-release battery that keeps its charge going and going.
长 — pictograph of long-haired person with cane
Originally a pictograph showing a person with long, flowing hair leaning on a cane, representing an elder. The meaning extended from 'long hair' to 'long' in general, and also to 'elder' or 'to grow' (read zhǎng). The modern form 长 is a simplification of the traditional 長.