效力
xiàolì · HSK 7
effect
💊 效 (effect) + 力 (force) = the force of an effect, its potency
效力 pairs 效 effect with 力 force or power. Together they mean the strength an effect carries, like the potency of medicine or the force of a rule taking hold.
力 — pictograph of a plow or arm muscle
力 originated as a pictograph of an ancient plow, the main tool requiring physical exertion in early agriculture. Some scholars also see it as a flexed arm showing muscle. From this concrete image it broadened to mean 'strength, power, force, effort'.