noun

• (firearms) A repeating firearm with three or more barrels grouped around a central axis.
  "She had her knees up, resting her wrists on them; the pepperbox muzzle of a flechette pistol emerged from her hands."
• (architecture) A tower capped by a cupola, looking similar to a giant pepper shaker.
  "Large, stately, and dark was its [the château's] outline against the dusky night-sky; there were pepper-boxes and tourelles and what-not fantastically going up into the dim starlight."
• (architecture, slang, chiefly in the plural) Any of the buildings of the Royal Academy and National Gallery in Trafalgar Square, London, having cupolas on the roof.
  "I also remember the old Royal Mews that stood on the site of the present trumpery National Gallery, with its too suggestive pepper-boxes; […]"