Source : Webster's Revised Unabridged Dictionary (1913)

Embankment \Em*bank"ment\, n.
   1. The act of surrounding or defending with a bank.

   2. A structure of earth, gravel, etc., raised to prevent
      water from overflowing a level tract of country, to retain
      water in a reservoir, or to carry a roadway, etc.

Source : WordNet®

embankment
     n : a long artificial mound of stone or earth; built to hold
         back water or to support a road or as protection