big cat vs cheetah

big cat

noun
  • Any large feline animal, especially one of the Panthera genus, including tigers, lions, jaguars and leopards. 

  • Used other than figuratively or idiomatically: see big, cat. 

cheetah

noun
  • A distinctive member (Acinonyx jubatus) of the cat family, slightly smaller than the leopard, but with proportionately longer limbs and a smaller head; native to Africa and southeast Asia (where it is nearly extinct) and also credited with being the fastest terrestrial animal. 

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