A stinger is a kind of alcoholic drink, or rather several kinds of entirely different make. Originally it was simply whisky and soda, half and half, much savoured by the British in Malaya, and the name comes from the Malay word setengah, 'half'. This mixed drink is also written as stengah or stingah.
The other kind of cocktail is so entirely different from a whisky-and-soda that I imagine it must be an independent invention, and perhaps given its coincidental name because it stings. This is brandy and creme de menthe, properly white or clear creame de menthe, with the brandy tending to predominate in quantity (recipes out there on the Web vary between 1:1 and 4:1).
These are not to be confused with a another alcohol with a sting, namely stingo, a kind of thick strong beer.
Then we get variations on these. The Louisville stinger sounds a bit stinging: bourbon, rum, creme de menthe, and creme de cacao. A royal stinger is a hybrid of the two stingers, whisky and white creme de menthe. Another possibility is to add vodka to the... well of course you can add anything you like, quite frankly; if you've got creme de menthe in there as a base you're not likely to be over-finicky about what else goes into it. So an amaretto stinger is creme de menthe and... urp, excuse me, gotta rush...