donkey vs wild horse

donkey

noun
  • A domestic animal, Equus asinus asinus, similar to a horse. 

  • A bad poker player. 

  • A fool. 

  • A small auxiliary engine. 

  • A stubborn person. 

wild horse

noun
  • A member of the species Equus ferus, sometimes excluding the domesticated horse. 

  • A feral horse. 

  • An untamed horse. 

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