folkyoudaoicibaDictYouDict[folk 词源字典]
folk: [OE] Folk comes from a prehistoric Germanic *folkam, which also produced German and Dutch volk and Swedish and Danish folk. It is not clear where this came from, although it has been linked with the Indo- European base *pel-, *plē- ‘fill’, which might also have produced Latin populus ‘people’. On the other hand Russian polk’, thought to have been borrowed from the Germanic form, means ‘division of an army’, and it is conceivable that this may preserve an earlier semantic stratum, represented also in Old Norse folk, which signified both ‘people’ and ‘army’.
[folk etymology, folk origin, 英语词源]
folk (n.)youdaoicibaDictYouDict
Old English folc "common people, laity; men; people, nation, tribe; multitude; troop, army," from Proto-Germanic *folkam (cognates: 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," 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." Superseded in most senses by people.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).