erosion


erosion (http://definr.com/erosion)

     n 1: the mechanical process of wearing or grinding something down
          (as by particles washing over it) [syn: eroding, {eating
          away}, wearing, wearing away]
     2: condition in which the earth's surface is worn away by the
        action of water and wind
     3: erosion by chemical action [syn: corrosion, corroding]