Machicolation

noun

2. A projecting gallery at the top of a castle wall, supported by a row of corbels and having openings in the floor through which stones and boiling liquids could be dropped on attackers.
3. One of these openings.
4. A row of small projecting arches used as an ornamental architectural feature.
5. In medieval architecture, an opening in the vault of a portal or passage, or in the floor of a projecting gallery, made for the purpose of hurling missiles, or pouring down molten lead, hot pitch, etc., upon an enemy essaying to enter or mine.