key

Explanation

1. key
An implement that is used to lock or unlock a door or lock.

2. clue
A clue with which one can solve a problem.

3. keyboard
A keyboard of a computer or typewriter, that inputs characters when pressed with fingers.

4. key
The part of a keyboard instrument such as a piano or harmonium, that makes sounds when pressed with fingers.

Examples
비상용 키
자동차 키
키가 맞다

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