Sentence:  Nanny Broome was looking up at the outer wall.  Just under the ceiling there were three lunette <WSD>windows</WSD>, heavily barred and blacked out in the normal way by centuries of grime. 
Meaning of the word marked with <WSD> tags:  An opening, usually covered by one or more panes of clear glass, to allow light and air from outside to enter a building or vehicle.