acclivity vs hummock

acclivity

noun
  • A slope or inclination of the earth, as the side of a hill, considered as ascending, in opposition to declivity, or descending; an upward slope; ascent. 

hummock

noun
  • A small hill; a hillock; a knoll. 

  • A fistful. 

  • A ridge or hill of ice in an ice field. 

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