作用
さよう · sayou · JLPT N1 · noun
function
作 — person radical 亻 + 乍
作 combines the person radical 亻 with 乍, which originally depicted a sudden action or making something. The character means 'to do, make, or create,' with 亻 indicating human activity and 乍 supplying the sound. Over time it broadened to cover works, deeds, and acting as something.
用 — pictograph of a bucket or wooden pail
用 originally depicted a bucket or container, possibly a sacrificial vessel made of wood. Over time it was borrowed to mean 'to use' or 'employ,' losing its concrete object sense. The modern meaning 'use' has been standard since early classical Chinese.