Something used for fastening, which can only be opened with a key or combination.

(by extension) A mutex or other token restricting access to a resource.

A segment of a canal or other waterway enclosed by gates, used for raising and lowering boats between levels.

To become fastened in place.

“If you put the brakes on too hard, the wheels will lock.”

To fasten with a lock.

“Remember to lock the door when you leave.”

To be capable of becoming fastened in place.

“This door locks with a key.”