crupper vs rear end

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. 

rear end

noun

  • The buttocks. 

  • The back or hindmost part of anything, such as a car. 

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