(esp in medieval castles) a projecting gallery or parapet supported on corbels having openings through which missiles could be dropped
2.
any such opening
machicolation in American English
(məˌtʃɪkəˈleɪʃən)
noun
1.
an opening in the floor of a projecting gallery or parapet, between the supports or corbels, or in the roof over an entrance, through which hot liquids, heavy stones, etc. could be dropped by the defenders of a fortress