Here in Oz horseracing we have betting on the winner: to win, the first 3 finishers in a race: a trifecta, the winners of 4 nominated races: a Quadrella, and the first 2 finishers in a race: A quinella. Etymonline and other internet searches show a Spanish influence and a game of 5 players but with the above definition. I see no suggestion as to how they got connected. Any thoughts on how something with a 5 in its name came to mean only 2? “Difecta”, “Bifecta” or “Duella” would make more sense.

Etymonline says:

quinella Look up quinella at Dictionary.com
form of betting in which the bettor picks the first and second horses in a given race, 1942, Amer.Eng., from Amer.Sp. quiniela, originally a ball game with five players, from L. quini “five each,” from quinque “five” (see quinque-). The sense evolution in Spanish was from the game to a wager on the scores of the players, hence “any wager against the house.”

Which doesn’t really explain why this term applied to that particular form of wager.

I was just thinking of this the other day when I saw “exacta” in Dave’s list.

EDIT: what an interesting world of words it is when an American Spanish word for one thing can become an English word for something else that no one outside of NZ/Aust has ever heard of, in such a short space of time.

It’s in the OED, which says quinella is originally from the States and from jai alai. Only later did it migrate to horseracing. It gives the etymology as being from “Spanish quina double five at dice.”

The citations include three U.S. citations ranging from 1902 to 2004, a 1974 one from New Zealand, and a 1977 one from the BBC, so it’s use doesn’t appear to be restricted to down under (despite what Wikipedia says).