The New York World, 1891, tells us that this is an Aztec word, and that “the liquor was discovered by a Toltec noble, who sent it to the king by the hand of his daughter Xochitl. The king fell in love with the maiden, drank the liquor, and called them xoc-tl, a name perpetuated by the word cocktail.”
Cocktail is an iced drink made of spirits mixed with bitters, sugar, and some aromatic flavouring. Champagne cocktail is champagne flavoured with Angostura bitters; soda cocktail is sodawater, sugar, and bitters.
“Did ye iver try a brandy cocktail, Cornel?” —Thackeray: The Newcomes, xiii.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894