What is the meaning of Pepperbox?

A pepper shaker.

A repeating firearm with three or more barrels grouped around a central axis.

A buttress at one side of the court in the game of fives.

A tower capped by a cupola, looking similar to a giant pepper shaker.

Any of the buildings of the Royal Academy and National Gallery in Trafalgar Square, London, having cupolas on the roof.

Source: wiktionary.org