intransitive verb
Definition: To become secured or fastened, often referring to doors or mechanisms that prevent movement.
Example: The door locks automatically when it is closed.
noun
Definition: A device that is used to secure something, usually operated by a key or combination, to keep it closed or safe.
Example: She turned the key to unlock the door after a long day at work.
transitive verb
Definition: To fasten something securely so that it cannot be opened or accessed without a key or combination.
Example: Please lock the door before you leave the house.