"terminal part of the leg of a vertebrate animal," Old English fot "foot," from Proto-Germanic *fōts (source also of Old Frisian fot, Old Saxon fot, Old Norse fotr, Danish fod, Swedish fot, Dutch voet, Old High German fuoz, German Fuß, Gothic fotus "foot"), from PIE root *ped- "foot." Plural form feet is an instance of i-mutation.
The linear measure was in Old English (the exact length has varied over time), this being considered the length of a man's foot; a unit of measure used widely and anciently. In this sense the plural is often foot. The current inch and foot are implied from measurements in 12c. English churches (Flinders Petrie, "Inductive Metrology"), but the most usual length of a "foot" in medieval England was the foot of 13.2 inches common throughout the ancient Mediterranean. The Anglo-Saxon foot apparently was between the two. All three correspond to units used by the Romans, and possibly all three lengths were picked up by the Anglo-Saxons from the Romano-Britons. "That the Saxon units should descend to mediæval times is most probable, as the Normans were a ruling, and not a working, class." [Flinders Petrie, 1877]. The medieval Paul's Foot (late 14c.) was a measuring standard cut into the base of a column at the old St. Paul's cathedral in London. The metrical foot (late Old English, translating Latin pes, Greek pous in the same sense) is commonly taken to represent one rise and one fall of a foot: keeping time according to some, dancing according to others.
In Middle English also "a person" (c. 1200), hence non-foot "nobody." Meaning "bottom or lowest part of anything eminent or upright" is from c. 1200. Of a bed, grave, etc., from c. 1300. On foot "by walking" is from c. 1300. To get off on the wrong foot is from 1905 (the right foot is by 1907); to put one's best foot foremost first recorded 1849 (Shakespeare has the better foot before, 1596); Middle English had evil-foot (adv.) "through mischance, unluckily." To put one's foot in (one's) mouth "say something stupid" is attested by 1942; the expression put (one's) foot in something "make a mess of it" is from 1823. To have one foot in the grave "be near death" is from 1844. Colloquial exclamation my foot! expressing "contemptuous contradiction" [OED] is attested by 1923, probably euphemistic for my ass in the same sense, which dates to 1796 (also see eyewash).
1937, coined in the fantasy tales of J.R.R. Tolkien (1892-1973).
On a blank leaf I scrawled: 'In a hole in the ground there lived a hobbit.' I did not and do not know why. [Tolkien, letter to W.H. Auden, dated 1955]
The word also turns up in a very long list of folkloric supernatural creatures in the writings of Michael Aislabie Denham (d. 1859) as an aside to his explanation that those born on Christmas Eve cannot see spirits. Denham was an early folklorist who concentrated on Northumberland, Durham, Westmoreland, Cumberland, the Isle of Man, and Scotland. This was printed in volume 2 of "The Denham Tracts" [ed. James Hardy, London: Folklore Society, 1895], a compilation of Denham's scattered publications.
What a happiness this must have been seventy or eighty years ago and upwards, to those chosen few who had the good luck to be born on the eve of this festival of all festivals; when the whole earth was so overrun with ghosts, boggles, bloody-bones, spirits, demons, ignis fatui, brownies, bugbears, black dogs, specters, shellycoats, scarecrows, witches, wizards, barguests, Robin-Goodfellows, hags, night-bats, scrags, breaknecks, fantasms, hobgoblins, hobhoulards, boggy-boes, dobbies, hob-thrusts, fetches, kelpies, warlocks, mock-beggars, mum-pokers, Jemmy-burties, urchins, satyrs, pans, fauns, sirens, tritons, centaurs, calcars, nymphs, imps, incubuses, spoorns, men-in-the-oak, hell-wains, fire-drakes, kit-a-can-sticks, Tom-tumblers, melch-dicks, larrs, kitty-witches, hobby-lanthorns, Dick-a-Tuesdays, Elf-fires, Gyl-burnt-tales, knockers, elves, rawheads, Meg-with-the-wads, old-shocks, ouphs, pad-foots, pixies, pictrees, giants, dwarfs, Tom-pokers, tutgots, snapdragons, sprets, spunks, conjurers, thurses, spurns, tantarrabobs, swaithes, tints, tod-lowries, Jack-in-the-Wads, mormos, changelings, redcaps, yeth-hounds, colt-pixies, Tom-thumbs, black-bugs, boggarts, scar-bugs, shag-foals, hodge-pochers, hob-thrushes, bugs, bull-beggars, bygorns, bolls, caddies, bomen, brags, wraiths, waffs, flay-boggarts, fiends, gallytrots, imps, gytrashes, patches, hob-and-lanthorns, gringes, boguests, bonelesses, Peg-powlers, pucks, fays, kidnappers, gallybeggars, hudskins, nickers, madcaps, trolls, robinets, friars' lanthorns, silkies, cauld-lads, death-hearses, goblins, hob-headlesses, bugaboos, kows, or cowes, nickies, nacks necks, waiths, miffies, buckies, ghouls, sylphs, guests, swarths, freiths, freits, gy-carlins Gyre-carling, pigmies, chittifaces, nixies, Jinny-burnt-tails, dudmen, hell-hounds, dopple-gangers, boggleboes, bogies, redmen, portunes, grants, hobbits, hobgoblins, brown-men, cowies, dunnies, wirrikows, alholdes, mannikins, follets, korreds, lubberkins, cluricauns, kobolds, leprechauns, kors, mares, korreds, puckles korigans, sylvans, succubuses, blackmen, shadows, banshees, lian-hanshees, clabbernappers, Gabriel-hounds, mawkins, doubles, corpse lights or candles, scrats, mahounds, trows, gnomes, sprites, fates, fiends, sibyls, nicknevins, whitewomen, fairies, thrummy-caps, cutties, and nisses, and apparitions of every shape, make, form, fashion, kind and description, that there was not a village in England that had not its own peculiar ghost. Nay, every lone tenement, castle, or mansion-house, which could boast of any antiquity had its bogle, its specter, or its knocker. The churches, churchyards, and crossroads were all haunted. Every green lane had its boulder-stone on which an apparition kept watch at night. Every common had its circle of fairies belonging to it. And there was scarcely a shepherd to be met with who had not seen a spirit!
[Emphasis added] It is curious that the name occurs nowhere else in folklore, and there is no evidence that Tolkien ever saw this. The word also was recorded from 1835 as "a term generally used in Wales to express a quantity made up of four Welsh pecks" [in English court records for Hughes vs. Humphreys, a weights-and-measures case]. Hobbitry attested from 1947.