One of the mysteries of the English language finally explained.
A lock having or operated by a pin; specifically (a) a lock having a pin on to which the hollow shank of a key fits; (b) a lock operated by a pin which, when inserted, prevents the opening of a sliding door or window.
Mid 19th century; earliest use found in Scientific American. From pin + lock.
pin lock/ˈpɪn lɒk/
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