"liquor distilled from the juice of sugar cane or molasses," 1650s, apparently a shortening of rumbullion (1651), rombostion (1652), words all of uncertain origin, but suspicion falls on rum (adj.) "excellent, fine, good, valuable;" the phrase rum bouse "good liquor" is attested from 1560s and through 17c. The English word was borrowed into Dutch, German, Swedish, Danish, Spanish, Portuguese, Italian, French, and Russian.
In the Library of Trinity College, Dublin, is a manuscript entitled "A briefe description of the Island of Barbados." It is undated but from internal evidence it must have been written about the year 1651. In describing the various drinks in vogue in Barbados, the writer says : "The chief fudling they make in the Island is Rumbullion alias Kill-Divill, and this is made of sugar canes distilled, a hot, hellish, and terrible liquor. ["The Etymology of the Word Rum," in Timehri, 1885]
Rum was used from c.1800 in North America as a general (hostile) name for intoxicating liquors, hence rum-runner and much other Prohibition-era slang.
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," 1871]
"excellent, fine, good, valuable," canting slang, 1560s, also rome, "fine," said to be from Romany rom "male, husband" (see Romany). A very common 16c. cant word (opposed to queer), as in rum kicks "Breeches of gold or silver brocade, or richly laced with gold or silver" [Grose, "Dictionary of the Vulgar Tongue," 1785].
By 1774 it also had come to mean rather the opposite: "odd, strange, bad, queer, spurious," perhaps because it had been so often used approvingly by rogues in reference to one another. Or perhaps this is a different word. This was the main sense after c. 1800.
Rom (or rum) and quier (or queer) enter largely into combination, thus--rom = gallant, fine, clever, excellent, strong; rom-bouse = wine or strong drink; rum-bite = a clever trick or fraud; rum-blowen = a handsome mistress; rum-bung = a full purse; rum-diver = a clever pickpocket; rum-padder = a well-mounted highwayman, etc.: also queere = base, roguish; queer-bung = an empty purse; queer-cole = bad money; queer-diver = a bungling pickpocket; queer-ken = a prison; queer-mort = a foundered whore, and so forth. [John S. Farmer, "Musa Pedestris," 1896]
1778, an arbitrary formation, one of what Farmer describes as "A class of colloquialisms compounded with an intensive prefix" (ram- or rum-), probably suggesting in part rum (adj.) in its old slang sense of "good, fine," and ramp (n.2). In this case apparently suggested by boisterous, robustious, bumptious, etc. Coined about the same time were rumbustical, rambumptious "conceited, self-assertive," rumgumptious "shrewd, bold, rash," rumblegumption, rambuskious "rough," rumstrugenous. Also compare ramshackle, rambunctious.
1700, "a distiller" (in colloquial rum-dropper), agent noun from drop (v.). Meaning "small tube from which liquid may be made to fall in drops" is by 1889.
type of rum-based Cuban cocktail, by 1946, from Cuban Spanish, a diminutive of mojo, a word for certain sauces and marinades; Ayto ("Diner's Dictionary") considers it to be "probably a reapplication of the Spanish adjective mojo 'wet,'" from mojar "to moisten, make wet," from Vulgar Latin *molliare"to soften by soaking," from Latin mollire "to soften" (see emollient).
I don't know who originated this one, but every bar in the West Indies serves it, practically every rum recipe booklet gives the formula for it, so my little collection of rum drinks would hardly be complete without it. Such popularity must be deserved, and it is. It's a swell drink! ["Trader Vic's Book of Food and Drink," 1946]