root (n.) Look up root at Dictionary.com
"underground part of a plant," late Old English rot, from a Scandinavian source akin to Old Norse rot "root," figuratively "cause, origin," from Proto-Germanic *wrot (cognates: 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 *wrad- (see radish (n.), and compare wort). The usual Old English words for "root" were wyrttruma and wyrtwala.

Figurative use is from c.1200. Of teeth, hair, etc., from early 13c. Mathematical sense is from 1550s. Philological sense from 1520s. Slang meaning "penis" is recorded from 1846. In U.S. black use, "a spell effected by magical properties of roots," 1935. To take root is from 1530s. Root beer, made from the extracts of various roots, first recorded 1841, American English; root doctor is from 1821. Root cap is from 1875.
root (v.1) Look up root at Dictionary.com
"dig with the snout," 1530s, from Middle English wroten "dig with the snout," from Old English wrotan "to root up," from Proto-Germanic *wrot- (cognates: 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."

Associated with the verb sense of root (n.). Extended sense of "poke about, pry" first recorded 1831. Phrase root hog or die "work or fail" first attested 1834, American English (in works of Davey Crockett, who noted it as an "old saying"). Reduplicated form rootin' tootin' "noisy, rambunctious" is recorded from 1875.
root (v.2) Look up root at Dictionary.com
"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.
root (v.3) Look up root at Dictionary.com
"fix or firmly attach by roots" (often figurative), early 13c., from root (n.); sense of "pull up by the root" (now usually uproot) also is from late 14c. Related: Rooted; rooting.