Origins: Cocktail

The word cocktail is a bit of an etymological puzzle: Originally only a nickname for an animal that rears up when irritated, by the late 1700s it had become another word for a horse with a “cocked” or shortened tail. But how or why it then made the leap to alcoholic mixed drinks in the early 1800s is a mystery.
One theory claims it’s to do with the drinks making you feel energized and sprightly, like an energetic horse, while another suggests it’s to do with cocktails being popular at the races. Alternatively, the two meanings could be entirely unrelated—one equally plausible explanation is that cocktail might in fact be an anglicized version of the French coquetier, meaning “egg-cup,” which was perhaps once used to serve the libations.
(Mental Floss)