The Collaborative International Dictionary of English v.0.48:

Escarpment \Es*carp"ment\, n. [Cf. F. escarpement.]
   A steep descent or declivity; steep face or edge of a ridge;
   ground about a fortified place, cut away nearly vertically to
   prevent hostile approach. See Scarp.
   [1913 Webster]

WordNet (r) 3.0 (2006):

escarpment
    n 1: a long steep slope or cliff at the edge of a plateau or
         ridge; usually formed by erosion [syn: escarpment,
         scarp]
    2: a steep artificial slope in front of a fortification [syn:
       escarpment, escarp, scarp, protective embankment]