Any high wall for defense.
In fortification: an indented parapet, formed by a series of rising members called cops or merlons, separated by openings called crenelles or embrasures, the soldier sheltering himself behind the merlon while he fires through the embrasure or through a loophole in the battlement.
The towering roof of heaven.
That which fortifies; especially, a work or works erected to defend a place against attack; a fortified place; a fortress; a fort; a castle.
A jagged pattern sometimes seen during an attack of migraine.
The act of fortifying; the art or science of fortifying places to strengthen defence against an enemy.
An increase in effectiveness, as by adding ingredients.