breastwork

noun

1. A fortification consisting of a breast-high bulwark; a parapet.

   “Before long we had flung enough sand-bags into place to make a low breastwork behind which the few men who were on this side of the position could lie down and fire.”

   “A cannonproof breastwork, built during the previous war, extended along the beach from the hills to the rocks.”

2. A railing on the quarter-deck and forecastle.

   “The Independencia is a two-turreted, breastwork ship of 9,000 tons displacement. […] The central breastwork is 130 feet in length at the top of the belt, and extends to the upper deck, 11 feet above the water-line. This breastwork incloses the boiler and engine hatches, the scuttles to magazines and shell-rooms, the principal openings for ventilation, and the two turrets.”

3. A parapet.

   “A swarthy boy opened a book and propped it nimbly under the breastwork of his satchel. He recited jerks of verse with odd glances at the text: […]”

4. (slang)Breast augmentation.