鍵
かぎ · kagi · JLPT N5 · noun
lock
🔑🔒 鍵 = metal 金 + build 建: a built metal device, the key or lock
The left side 金 marks metal objects; the right side 建 (build) originally gave the sound. Sound hook: kagi is close to cagey, and a cagey person keeps everything under lock and key. In Japanese the one word covers both the key and the lock.