alley cat vs big cat

alley cat

noun
  • An urban feral cat. 

  • A slut, a sexually promiscuous woman or prostitute. 

big cat

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

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

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