Physical key for a lock. Also used metaphorically for something that provides access or a solution.
I forgot my house key.
Where is the key to this box?
Refers to the locking mechanism itself, often used in contexts like 鍵をかける (to lock).
See also: 錠
Please lock the door.
key (to a problem, success, etc.); clue
Figurative use: the crucial element for solving a problem or achieving something.
The key to success is hard work.
A person who holds the key to the case.
He unlocked the room and went inside.
I ended up losing the key to my house.
I handed the room key to the building manager.
This technology will be the key to the negotiation's success.
key-shaped