"underground, downward-growing part of a plant," late Old English rōt and in part from a Scandinavian cognate akin to Old Norse rot "root," figuratively "cause, origin," from Proto-Germanic *wrot (source also of Old English wyrt "root, herb, plant," Old High German wurz, German Wurz "a plant," Gothic waurts "a root," with characteristic Scandinavian loss of -w- before -r-), from PIE root *wrād- "branch, root" (source of wort and radical). The usual Old English words for "root" were wyrttruma and wyrtwala.
Figurative use, "source of a quality or condition," is from late 12c. Of the base parts of teeth, hair, etc., from early 13c. Mathematical sense is from 1550s. Philological sense from 1520s. Slang meaning "penis" is recorded from 1846. In African-American vernacular use, "a spell effected by magical properties of roots," by 1935. The sense of "person considered as the source or offspring of a family or clan" is by early 14c., chiefly biblical.
For coveteousnes is the rote of all evylle, which whill some lusted after, they erde from the feyth, and tanglyd themselves with many sorowes. [I Timothy vi in Tyndale, 1526]
To take root is from mid-15c. as "settle in the ground," hence figurative use (by 1530s). Root beer, made from the extracts of various roots (sarsaparilla, sassafras, etc.), is recorded by 1841, American English; root doctor is from 1821. Roots "established ties with a locality or region; one's background or cultural origins" is by 1921.
"dig with the snout," 1530s, wroot, of swine, from Middle English wroten "dig with the snout," from Old English wrotan "to root up," from Proto-Germanic *wrot- (source also of Old Norse rota, Swedish rota "to dig out, root," Middle Low German wroten, Middle Dutch wroeten, Old High German ruozian "to plow up"), from PIE root *wrod- "to root, gnaw."
Altered by association with root (v.3), as if "to dig up by the roots." Extended sense of "poke about, pry" is recorded by 1831. The picturesque phrase root hog or die "work or fail" first attested 1834, American English (in works of Davy Crockett, who noted it as an "old saying").
"cheer, support," 1889, American English, originally in a baseball context, probably from root (v.1) via intermediate sense of "study, work hard" (1856). Related: Rooted; rooting.