Etymology
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hillbilly (n.)

"southern Appalachian person," by 1892, from hill (n.) + Billy/Billie, popular or pet form of William. In reference to a type of U.S. folk music, first attested 1924.

I would hate to see some old railroad man come here and take my job, and then, I don't think it is right to hire some Hill Billy and give him the same right as I just because he was hired the same time I was. [The Railroad Trainmen's Journal, vol. ix, July 1892]
In short, a Hill-Billie is a free and untrammelled white citizen of Alabama, who lives in the hills, has no means to speak of, dresses as he can, talks as he pleases, drinks whiskey when he gets it, and fires of his revolver as the fancy takes him. [New York Journal, April 23, 1900]

In Scott's collection of Border ballads, billie is a frequent term of address or intimacy, "comrade, companion, a brother in arms," "a term expressive of affection and familiarity" also "a brother; a wooer of a woman," and generally "a young man" [Jamieson, 2nd edition]. It is said to be a variant of bully (n.) in its old sense of  "sweetheart," also "fine fellow."

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rockabilly (n.)

type of popular music blending elements of rock 'n' roll and hillbilly music, 1956, from rock (n.2) in the music sense + second element abstracted from hillbilly music. One of the first uses is in a Billboard magazine item about Johnny Burnette's "Lonesome Train."

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ridge (n.)

Middle English rigge, from Old English hrycg "back of a man or beast," probably reinforced by Old Norse hryggr "back, ridge," from Proto-Germanic *hruggin (source also of Old Frisian hregg, Old Saxon hruggi, Dutch rug, Old High German hrukki, German Rücken "the back"). OED says "of uncertain relationship;" Pokorny, Boutkan, and Watkins have it from PIE *kreuk-, extended form of root *sker- (2) "to turn, bend."

The original "back" sense, predominant in Middle English, seems to have become archaic 17c. Also in Old English, "the top or crest of anything," especially when long and narrow, based on resemblance to the projecting part of the back of a quadruped, the "ridge" of the backbone. Probably also in late Old English "a long elevation of land, a long, narrow range of hills," implied in place-names. From late 14c. of the highest part of the roof of a building, also the strip of ground thrown up between two plowed furrows. The spelling with -dg- is from late 15c.

Ridge-runner, somewhat derisive term for "Southern Appalachian person, hillbilly," especially an upland white farmer of the Ozarks region, is recorded by 1917 (it later came into use in other regions). Also "person who wanders from place to place," often with a suggestion of illicit intent (1930).

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tacky (adj.2)

"in poor taste," 1888, from earlier sense of "shabby, seedy" (1862), adjectival use of tackey (n.) "ill-fed or neglected horse" (1800), later extended to persons in like condition, "hillbilly, cracker" (1888), of uncertain origin. Related: Tackiness.

The word "tacky" is a Southern colloquialism. It was coined by a wealthier or more refined and educated class for general application to those who were not sheltered by the branches of a family tree, who were "tainted." Those who were wealthy and yet had no great-grandfathers were "tackies." The word was used both in contempt and in derision. It is now nearly obsolete in both senses. There are no aristocrats in the South now, and therefore no "tackies." No man who has the instincts of a gentleman is spoken of as a "tacky," whether he can remember the name of his grandfather's uncle or not. But it has its uses. It is employed in describing persons of low ideas and vulgar manners, whether rich or poor. It may mean an absence of style. In dress, anything that is tawdry is "tacky." A ribbon on the shopkeeper's counter, a curtain in the bolt, a shawl or bonnet, a bolt of cloth fresh from the loom may be "tacky," because it is cheap and yet pretentious. In Louisiana the inferior grade of Creole ponies are known as "tackies." [Horace Ingraham, Charleston, S.C., in American Notes and Queries, Feb. 15, 1890]
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