He [Harry] stopped a passing guard, but didn't dare mention platform nine and three-quarters. The guard had never heard of Hogwarts and when Harry couldn't even tell him what part of the country it was in, he started to get annoyed, as though Harry was being stupid on purpose.
(Harry Potter and the Sorcerer's Stone)

What does ‘guard’ mean: 9 or 20 in a dictionary or any other?
9.a person or group of persons that guards, protects, or keeps a protective or restraining watch.
20. British . a railroad conductor.