rum (n.) Look up rum at Dictionary.com
"liquor from sugar cane or molasses," 1650s, shortening of rumbullion (1651), rombostion (1652), of uncertain origin, perhaps from rum (adj.).
The chiefe fudling they make in the Island [i.e. Barbados] is Rumbullion alias Kill-Devill, and this is made of suggar cane distilled, a hott, hellish and terrible liquor. ["A briefe Description of the Island of Barbados," 1651]
The English word was borrowed into Dutch, German, Swedish, Danish, Spanish, Portuguese, Italian, French, and Russian. Used since 1800 in North America as a general (hostile) name for intoxicating liquors.
Rum I take to be the name which unwashed moralists apply alike to the product distilled from molasses and the noblest juices of the vineyard. Burgundy in "all its sunset glow" is rum. Champagne, soul of "the foaming grape of Eastern France," is rum. ... Sir, I repudiate the loathsome vulgarism as an insult to the first miracle wrought by the Founder of our religion! [Oliver Wendell Holmes, "The Autocrat of the Breakfast-Table," 1891]
rum (adj.) Look up rum at Dictionary.com
"excellent, fine, good, valuable," 1560s, from rome "fine" (1560s), said to be from Romany rom "male, husband" (see Romany). E.g. rum kicks "Breeches of gold or silver brocade, or richly laced with gold or silver" [Grose, "Dictionary of the Vulgar Tongue," 1785].

A very common 16c. cant word, by 1774 it also had come to mean "odd, strange, bad, spurious," perhaps because it had been so often used approvingly by rogues in reference to one another. This was the main sense after c.1800.