arris vs hummock

arris

noun
  • Buttocks, arse. 

  • A ridge formed on the surface of flaked stone, such as a arrowhead or hand axe, as the result of the intersection of two or more flake removals. 

  • A sharp edge or ridge formed by the intersection of two surfaces 

  • A sharp edge or ridge formed by the intersection of two curved surfaces 

hummock

noun
  • A fistful. 

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

  • A small hill; a hillock; a knoll. 

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