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]

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "escarpment":
   abatis, advanced work, balistraria, bank, banquette,
   barbed-wire entanglement, barbican, barricade, barrier, bartizan,
   bastion, battlement, bluff, breastwork, bulwark, casemate,
   cheval-de-frise, circumvallation, cliff, contravallation,
   counterscarp, crag, curtain, demibastion, dike, drawbridge,
   earthwork, enclosure, entanglement, escarp, face, fence, fieldwork,
   fortalice, fortification, glacis, loophole, lunette, machicolation,
   mantelet, merlon, mound, outwork, palisade, palisades, parados,
   parapet, portcullis, postern gate, precipice, rampart, ravelin,
   redan, redoubt, sally port, scar, scarp, sconce, steep, stockade,
   tenaille, vallation, vallum, wall, work