Mind you, just because some site on the web says it's so and even gives a reference, it ain't necessarily so. The Diccionario Castellano of 1787 may well have that definition. But that link Dicho gave isn't to the Diccionario Castellano of 1787. It's to a site talking about it.

So there's still the possibility that some joker might have made it up, and planted it somewhere where that the way some joker faked an 19th century version of The Fields of Athenry.

And that doesn't mean I'm clinging on to that song explanation, just that this seems like a good opportunity for someone to chase up the actual references and pin down the facts. Maybe Escamillo could sort it for us?