Etymology
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bay (adj.)
"reddish-brown," usually of horses, mid-14c., from Anglo-French bai (13c.), Old French bai, from Latin badius "chestnut-brown" (used only of horses), from PIE root *badyo- "yellow, brown" (source also of Old Irish buide "yellow"). As a noun, elliptical for a horse of this color.
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bay (n.4)

laurel shrub (Laurus nobilis, source of the bay-leaf), late 14c., but meaning originally only the berry, from Old French baie (12c.) "berry, seed," from Latin baca, bacca "berry, fruit of a tree or shrub, nut" (source also of Spanish baya, Old Spanish bacca, Italian bacca "a berry"), a word of uncertain origin. De Vaan writes that connection with Greek Bakhos "Bacchus" is difficult, as the Greek word probably was borrowed from an Asian language. Some linguists compare Berber *bqa "blackberry, mulberry," and suggest a common borrowing from a lost Mediterranean language.

Extension of the word to the shrub itself is from 1520s. The leaves or sprigs were woven as wreaths for conquerors or poets, hence "honorary crown or garland bestowed as a prize for victory or excellence" (1560s). Bay-leaf is from 1630s. Bay-berry (1570s) was coined after the sense of the original word had shifted to the tree.

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bay (v.)
"to bark or howl (at)," late 14c., from bay (n.3). Related: Bayed; baying.
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bay (n.1)
"inlet, recess in the shore of a sea or lake," c. 1400, from Old French baie, Late Latin baia (source of Spanish and Portuguese bahia, Italian baja), which is perhaps ultimately from Iberian (Celtic) bahia.
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bay (n.2)
"opening in a wall," especially a space between two columns, late 14c. from Old French baee "opening, hole, gulf," noun use of fem. past participle of bayer "to gape, yawn," from Medieval Latin batare "gape," perhaps of imitative origin. Meaning "compartment for storage: is from 1550s. Somewhat confused with bay (n.1) "inlet of the sea," it is the bay in sick-bay and bay window (early 15c.).
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bay (n.3)
"deep-toned howl of a dog," early 14c., earlier "howling chorus raised (by hounds) when in contact with the hunted animal," c. 1300, from Old French bayer, from PIE root *bai- echoic of howling (compare Greek bauzein, Latin baubari "to bark," English bow-wow; also see bawl).

From the condition of a hunted animal comes the transferred sense of "final encounter," and thence, on the notion of turning to face the danger when further flight or escape is impossible, at bay.
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rum (n.)

"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]
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rum (adj.)

"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]
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rum-runner (n.)
"smuggler or transporter of illicit liquor," 1919, from rum (n.) + runner.
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at bay (prep.)
late 14c., originally often at the bay; see bay (n.3). Figurative use, of human beings in difficulties, is from c. 1400. The expression reflects the former more widespread use of at. The earlier form of the phrase was at abai, used of hunted animals, "unable to escape," c. 1300, from French.
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