"the root of the beet plant," 1570s, from beet (n.) + root (n.).
Entries linking to beet-root
beet n.
plant growing wild in northern Europe, cultivated for use of its succulent root as food and for sugar extraction, Old English bete "beet, beetroot," from Latin beta, which is said to be of Celtic origin. Common in Old English, then lost till c. 1400. Still usually spoken of in plural in U.S. A general West Germanic borrowing, cognates: Old Frisian bete, Middle Dutch bete, Old High German bieza, German Beete.
root n.
"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.