escarp vs escarpment

escarp

noun
  • The side of the ditch next to the parapet in a fortification; the scarp. 

verb
  • To make into, or furnish with, a steep slope, like that of a scarp. 

escarpment

noun
  • 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. 

How often have the words escarp and escarpment occurred in a corpus of books? (source: Google Ngram Viewer )