croup vs crupper

croup

noun
  • The top of the rump of a horse or other quadruped. 

  • An infectious illness of the larynx, especially in young children, causing respiratory difficulty. 

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. 

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