Killing (“make a killing”)

To “make a killing” means to make a large (and usually quick) profit. “Make a killing” has been cited in print since at least 1887, when it was used in horseracing.
 
The saying “make a living, not a killing” has been cited in print since at least 1959.
 
   
Wiktionary: make a killing
Verb
to make a killing
1.(idiomatic) To win or earn a large amount of money
 
The Free Dictionary
make a killing
Fig. to have a great success, especially in making money.
 
GoogleBooks
Cassell’s Dictionary of Slang
By Jonathon Green
Cassell
2006
Pg. 917:
make a killing v. (also make a cleaning, make a kill) [late 19C+] (orig. US) to make a profit by gambling, whether at the races, on the stock market, in a casino etc.
   
(Oxford English Dictionary)
killing, n.
A large profit; a quick and profitable success in business, etc. slang (orig. U.S.).
1888 Texas Siftings 24 Mar. 13/2   Fred Jarvis‥getting $15,000 in The Louisiana State Lottery drawing.‥ Many‥would like to know something relative to the man who was fortunate enough to ‘make a killing’.
1912 T. Dreiser Financier xxx. 340   Railroad securities‥were considered weak under the present circumstances, and a great killing was expected.
1938 ‘N. Shute’ Ruined City i. 11   I’m a banker, of course. I don’t take tips, and I don’t make any great killings, but in my quiet way I get along all right.
 
7 August 1887, Cleveland (OH) Plain Dealer, “Turf,” pg. 6, col. 1:
Of course he didn’t win. But further down on the circuit, when the times are right, the shrewd ones will make “a killing.”
   
Google Books
Saddle and Mocassin
By Francis Francis
London: Chapman and Hall
1887
Pg. 238:
Are we going to ‘make a killing,’ or to buy a ranch, or only to steal some cattle? And what’s the matter with our stopping here, and living comfortably, until you get back?
 
10 May 1888, New York (NY) Times, “Kentucky’s Derby.” pg. 3:
He has been running second or unplaced in a number of races of late, but there is good reason for thinking this has been done for the purpose of depreciating his stock in the Derby and affording his owners a chance to make a “killing” on the great Kentucky event.