lock

A lock is a metal thing on a door (or on a window, drawer, etc.) that stops people from opening the door unless they have the right key to open it.

Example: No one will take things from my house. I have a very strong lock on the door.

A lock is two or more gates (doors) in water to let boats move from lower water to higher water or the other way.

Someone locks a door when they close the lock with a key so that no one can come in.

Example: Remember to lock the door when you leave the house.