idiom. Add to word list Add to word list. locked away safely: Her jewelry is securely under lock and key at the bank. If a person, especially a criminal, is under lock and key, they are being kept in a place from which they cannot escape, usually a prison.

The key serves as a security token for access to the locked area; locks are meant to only allow persons having the correct key to open it and gain access. In more complex mechanical lock/key systems, two different keys, one of which is known as the master key, serve to open the lock.

If it has teeth on both sides it's for a car, if it's tiny it's for a padlock, if it's regular size it's likely for a door. A house key or residential door key will have a code like "LR-2" or "SR-1" on the head.