crupper vs nates

crupper

noun
  • The buttocks or rump, especially of a horse. 

  • A strap, looped under a horse's tail, used to stop a saddle from slipping. 

  • A piece of armour covering the hindquarters/buttocks of a horse. 

verb
  • To fit with a crupper; to place a crupper upon. 

nates

noun
  • The buttocks. 

  • The umbones of a bivalve shell. 

  • The two anterior of the four lobes on the dorsal side of the midbrain of most mammals; the anterior optic lobes. 

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