Source : Webster's Revised Unabridged Dictionary (1913)

Breastwork \Breast"work`\ (br[e^]st"w[^u]rk`), n.
   1. (Fort.) A defensive work of moderate height, hastily
      thrown up, of earth or other material.

   2. (Naut.) A railing on the quarter-deck and forecastle.

Source : WordNet®

breastwork
     n : fortification consisting of a low wall [syn: {parapet}]