応用
おうよう · ouyou · JLPT N2 · noun
application
🛠️ 応 respond + 用 use = answer a real situation by using what you know
応 also appears in 反応 (reaction) and 対応 (dealing with something), and 用 in 利用 (use). ouyou sounds like oh, yo-yo: once you know the basic spin, you put it to use in tricks. That is 応用, as in 応用問題 (applied problems).
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.