Make A Killing Meaning

(idiomatic) To win or earn a large amount of money.

Example: 1913, Rex Ellingwood Beach, The Iron Trail: An Alaskan Romance, ch. 5:
  "Now if they were playing faro I could make a killing."
2009, Tom Huddleston, "What's all the fuss about 'Slumdog Millionaire'?," Time, 17 Jan.:
  Danny Boyle's critical darling 'Slumdog Millionaire' has made a killing at the box office and is now being lavished with awards.