锁 (suǒ): để khóa

I was in such a hurry when I left the house that I forgot to lock the door, and as a result I spent the whole day worrying that a thief might get in.

For safety's sake, my mother checks every night before going to bed whether the windows are properly locked.

The lock on my bicycle was broken, so I had to leave it by the roadside and walk home.

He inserted the key into the lock, but it wouldn't turn; on closer inspection, it turned out he had taken the wrong key.

The cabinets in this shop are all locked; if customers need something, they have to ask a salesperson to open them.