machicolation

noun Architecture.

1. an opening in the floor between the corbels of a projecting gallery or parapet, as on a wall or in the vault of a passage, through which missiles, molten lead, etc., might be cast upon an enemy beneath.
2. a projecting gallery or parapet with such openings.

noun

1. (esp in medieval castles) a projecting gallery or parapet supported on corbels having openings through which missiles could be dropped
2. any such opening