Machicolation n. : An opening between the corbels which support a projecting parapet, or in the floor of a gallery or the roof of a portal, shooting or dropping missiles upen assailants attacking the base of the walls. Also, the construction of such defenses, in general, when of this character. See Illusts. of Battlement and Castle.

Machicolation n. : The act of discharging missiles or pouring burning or melted substances upon assailants through such apertures.

Example:


Taxonomy
Machicolation, free encyclopedia, machicolations, hoardings, battlement, stone, Further reading, search, attackers, design, the Middle Ages, outwards, supporting wall, made of wood, siege, Advantages, Old Provençal, collum.

Defination from the web:
machicolation is a floor opening between the supporting corbels of a battlement, through which stones could be dropped on attackers at the base ... Machicolation was later used for decorative effect with spaces between the corbels but without the openings, and subsequently became a ...