A notched and grooved, usually metal implement that is turned to open or close a lock.
예문
1. all in the same key (모두 같은 목소리로, 단조롭게) 2. major key (장조) 3. the key to happiness (행복을 얻는 비결) 4. the key to trainning a horse (말을 훈련시키는 방법) 5. in a minor key (침울한 어조로)
