Source : Webster's Revised Unabridged Dictionary (1913)

Earthwork \Earth"work`\, n.
   1. (Mil.) Any construction, whether a temporary breastwork or
      permanent fortification, for attack or defense, the
      material of which is chiefly earth.

   2. (Engin.)
      (a) The operation connected with excavations and
          embankments of earth in preparing foundations of
          buildings, in constructing canals, railroads, etc.
      (b) An embankment or construction made of earth.

Source : WordNet®

earthwork
     n : an earthen rampart