Jonathan Yardley writes in the Washington Post:

[..]Rum is essentially an accident. On 17th-century sugar plantations in the Caribbean, "sugar wastes were considerable," chief among them molasses. Eventually, someone figured out that molasses combined with other ingredients could produce a potent if rather vile alcoholic drink that came to be called rum, perhaps as "a truncated version of rumbullion or rumbustion ," both of which "were British slang for 'tumult' or 'uproar,' " which, as Curtis puts it, conjures up images of "fractious islanders cracking one another over the head in rumbustious entanglements at island tippling houses."[..]

Read the entire article.