Railing (7)
'railing' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for parapet that I've seen before include "Low wall along the side of a bridge" , "defensive position" , "keep overlooking this?" , "Low wall (on bridge, roof, etc)" , "Militarily, it protects" .)
'railing' is the definition.
(balustrade is a kind of railing)
This is all the clue.
(Other definitions for balustrade that I've seen before include "Form of railing" , "feature of terrace, perhaps" , "Railing on stairs or balcony" , "Row of short pillars with coping" , "Row of pillars under rail" .)