Wiktionary
vb. (context idiomatic English) To win or earn a large amount of money.
Usage examples of "make a killing".
Even swindlers could make a killing, saying one thing that meant another altogether, which the dude would find out too late, once his money or land or horse or whatever he'd risked was long out of his possession.
I thought I had a chance to make a killing, clean up a lot of old debts….
They had arranged, through some little vagaries of the wheel, vagaries that could be brought out by the assistance of the croupier, that apparently Texas should make a killing.
We're gonna make a killing -- no lousy five-buck-an-hour job for us -- no offense.
If it were not, one could make a killing on the stock exchange by having a computer that would remember tomorrow’.
The Uzbek traded mostly among the more fundamentalist IF brigades, who wouldn't drink the vodka anyway, and the Russian would make a killing from his alcoholic and lonely compatriots.