Source : Webster's Revised Unabridged Dictionary (1913)

Counterguard \Coun"ter*guard`\ (koun"t[~e]r*g[aum]rd`), n.
   (Fort.)
   A low outwork before a bastion or ravelin, consisting of two
   lines of rampart parallel to the faces of the bastion, and
   protecting them from a breaching fire.