Old English folc "common people, laity; men; people, nation, tribe; multitude; troop, army," from Proto-Germanic *fulka- (source also of Old Saxon folc, Old Frisian folk, Middle Dutch volc, Dutch volk, Old High German folc, German Volk "people"). Perhaps originally "host of warriors:" Compare Old Norse folk "people," also "army, detachment;" and Lithuanian pulkas "crowd," Old Church Slavonic pluku "division of an army" (hence Russian polk "regiment"), both believed to have been borrowed from Proto-Germanic. Old English folcstede could mean both "dwelling-place" and "battlefield." According to Watkins, from PIE *ple-go-, suffixed form of root *pele- (1) "to fill," which would make it cognate with Greek plethos "people, multitude," and Latin plebes, "the populace, the common people." Boutkan thinks both the Germanic and Balto-Slavic could be a common borrowing from a substrate language.
Superseded in most senses by people. Generally a collective noun in Middle English, however plural folks is attested from 15c. Old English folc was commonly used in forming compounds (59 are listed in the Clark Hall dictionary), such as folccwide "popular saying," folcgemot "town or district meeting;" folcwoh "deception of the public." Modern use of folk as an adjective is from c. 1850 (see folklore).
By Folk-etymology is meant the influence exercised upon words, both as to their form and meaning, by the popular use and misuse of them. In a special sense, it is intended to denote the corruption which words undergo, owing either to false ideas about their derivation, or to a mistaken analogy with other words to which they are supposed to be related. [The Rev. A. Smythe Palmer, "Folk-Etymology," 1882]
"music of the people," 1852 (Andrew Hamilton, "Sixteen Months in the Danish Isles"), from folk in the "of the people" sense (also see folklore) + music. Modeled on German Volksmusik. In reference to a branch of modern popular music imitative of the simple and artless style of music originating among the common people (originally associated with Greenwich Village in New York City) it dates from 1958.
Of airs properly national, it should be remembered, the composers are not known. They are found existing among the people, who are ignorant of their origin. They are, to borrow a German phrase, folk-music. [Richard Grant White, "National Hymns," New York, 1861]
The term National Music implies that music, which, appertaining to a nation or tribe, whose individual emotions and passions it expresses, exhibits certain peculiarities more or less characteristic, which distinguish it from the music of any other nation or tribe.*
* The Germans call it Volksmusik, a designation which is very appropriate, and which I should have rendered folk-music, had this word been admissible. [Carl Engel, "An Introduction to the Study of National Music," London, 1866]