noun
Physical key for a lock. Also used metaphorically for something that provides access or a solution.
家の鍵を忘れてしまった。
I forgot my house key.
この箱の鍵はどこですか。
Where is the key to this box?
noun
Refers to the locking mechanism itself, often used in contexts like 鍵をかける (to lock).
See also: 錠
ドアに鍵をかけてください。
Please lock the door.
noun
key (to a problem, success, etc.); clue
Figurative use: the crucial element for solving a problem or achieving something.
成功の鍵は努力だ。
The key to success is hard work.
事件の鍵を握る人物。
A person who holds the key to the case.