parapet

noun

• a low protective wall along the edge of a roof, bridge, or balcony: she stood on the bridge, leaning over the parapet to watch the water race by
• a protective wall or earth defence along the top of a trench or other place of concealment for troops: the sandbags that made up the parapet had been blown away and the wall of the trench had caved in figurativeMr Scargill raised his head above the parapet to call for the repeal of ‘anti-union’ legislation