Online Etymology Dictionary

busybody (n.): "meddlesome person," 1520s, from busy (adj.) in the otherwise-obsolete sense "prying, meddlesome" + body "person."
busyness (n.): 1849, first attested in Thoreau, from busy (adj.) + -ness. A modern formation made necessary after business evolved away from busy.
but (adv., prep.): Old English butan, buton "unless, except; without, outside," from West Germanic *be-utan, a compound of *be- "by" (see by) + *utana "out, outside; from without," from ut "out" (see out (adv.)). Not used as a conjunction in Old English. As a noun from late 14c.
butane (n.): paraffin hydrocarbon, 1875, from butyl, hydrocarbon from butyric acid, a product of fermentation found in rancid butter, from Latin butyrum (see butter (n.)) + chemical suffix -ane.
butch (n.): "tough youth," 1902, first attested in nickname of U.S. outlaw George Cassidy (1866-?), probably an abbreviation of butcher (n.). Sense of "aggressive lesbian" is 1940s.
butcher (v.): 1560s, from butcher (n.). Related: Butchered; butchering. Re-nouned 1640s as butcherer.
butcher (n.): c.1300, from Anglo-French boucher, from Old French bochier "butcher, executioner" (12c., Modern French boucher), probably literally "slaughterer of goats," from bouc "male goat," from Frankish *bukk or some other Germanic source (see buck (n.1)) or Celtic *bukkos "he-goat." Figurative sense of "brutal murderer" is attested from 1520s. Butcher-knife attested from 18c. Related: Butcherly.
butchery (n.): "the trade of a butcher," mid-15c., bocherie, from Old French bocherie (13c., Modern French boucherie), from bochier (see butcher (n.)).
butler (n.): late 12c., from Anglo-French buteillier "cup-bearer," from Old French boteillier "cup-bearer, butler, officer in charge of wine," from boteille "wine vessel, bottle" (see bottle (n.)). The word reflects the position's original function as "chief servant in charge of wine." In Old French, fem. boteilliere was used of the Virgin Mary as "dispenser" of the cup of Mercy.
butt (n.1): "thick end," c.1400, butte, which probably is related to Middle Dutch and Dutch bot, Low German butt "blunt, dull," Old Norse bauta (see beat (v.)). Or related somehow to Old English buttuc "end, small piece of land," and Old Norse butr "short." In sense of "human posterior" it is recorded from mid-15c. Meaning "remainder of a smoked cigarette" first recorded 1847.
butt (n.2): "liquor barrel," late 14c., from Anglo-French but and Old French bot "barrel, wineskin" (14c., Modern French botte), from Late Latin buttis "cask" (see bottle (n.)). Cognate with Spanish and Portuguese bota, Italian botte. Usually a cask holding 108 to 140 gallons, or roughly two hogsheads, but the measure varied greatly.
butt (n.3): "target of a joke," 1610s, originally "target for shooting practice" (mid-14c.), from Old French but "aim, goal, end, target (of an arrow, etc.)," 13c., which seems to be a fusion of Old French words for "end" (bout) and "aim, goal" (but), both ultimately from Germanic. The latter is from Frankish *but "stump, stock, block," or some other Germanic source (cf. Old Norse butr "log of wood"), which would connect it with butt (n.1).
butt (v.): "hit with the head," c.1200, from Anglo-French buter, from Old French boter "to push, shove, knock; to thrust against," from Frankish or another Germanic source (cf. Old Norse bauta, Low German boten "to strike, beat"), from Proto-Germanic *butan, from PIE root *bhau- "to strike" (see batter (v.)). Related: Butted; butting. To butt in "rudely intrude" is American English, attested from 1900.
butt (n.4): "flat fish," c.1300, a general Germanic name applied to various kinds of flat fishes; cf. Old Swedish but "flatfish," German Butte, Dutch bot, perhaps ultimately related to butt (n.1). "Hence butt-woman, who sells these, a fish-wife." [OED]
butte (n.): 1805, American English, from French butte, from Old French but "mound, knoll" (see butt (n.3)). A French word introduced in Lewis & Clark's journals.
butter (n.): Old English butere "butter," general West Germanic (cf. Old Frisian, Old High German butera, German Butter, Dutch boter), an early loan-word from Latin butyrum "butter" (source of Italian burro, Old French burre, French beurre), from Greek boutyron, perhaps literally "cow-cheese," from bous "ox, cow" (see cow (n.)) + tyros "cheese;" but this might be a folk etymology of a Scythian word.

The product was used from an early date in India, Iran and northern Europe, but not in ancient Greece and Rome. Herodotus described it (along with cannabis) among the oddities of the Scythians. Butter-knife attested from 1818.
butter (v.): Old English buterian "spread butter on," from the same source as butter (n.). Figurative meaning "to flatter lavishly" is by 1798 (with up (adv.), in Connelly's Spanish-English dictionary, p.413). Related: Buttered; buttering.
butter-fingered (adj.): "apt to let things fall," 1610s, from butter (n.) + finger (n.).
buttercup (n.): type of small wildflower with a yellow bloom, 1777, from a merger of two older names, gold-cups and butterflower. See butter (n.) + cup (n.).
butterfingers (n.): "person apt to let things fall," 1837; see butter-fingered.
butterfly (n.): Old English buttorfleoge, evidently butter (n.) + fly (n.), but of obscure signification. Perhaps based on the old notion that the insects (or witches disguised as butterflies) consume butter or milk that is left uncovered. Or, less creatively, simply because the pale yellow color of many species' wings suggests the color of butter. Another theory connects it to the color of the insect's excrement, based on Dutch cognate boterschijte. An overview of words for "butterfly" in various languages can be found here. Also see papillon.

Applied to persons from c.1600, originally in reference to vain and gaudy attire; by 1806 in reference to transformation from early lowly state; in reference to flitting tendencies by 1873. The swimming stroke so called from 1936. Butterflies "light stomach spasms caused by anxiety" is from 1908.
The butterfly effect is a deceptively simple insight extracted from a complex modern field. As a low-profile assistant professor in MIT's department of meteorology in 1961, [Edward] Lorenz created an early computer program to simulate weather. One day he changed one of a dozen numbers representing atmospheric conditions, from .506127 to .506. That tiny alteration utterly transformed his long-term forecast, a point Lorenz amplified in his 1972 paper, "Predictability: Does the Flap of a Butterfly's Wings in Brazil Set Off a Tornado in Texas?" [Peter Dizikes, "The Meaning of the Butterfly," The Boston Globe, June 8, 2008]
buttermilk (n.): 1520s, from butter (n.) + milk (n.). Cf. German Buttermilch. It is what remains after the butter has been churned out.
butternut (n.): also butter-nut, 1753, nut of the white walnut, a North American tree; transferred to the tree itself from 1783. The nut's color was a brownish-gray, hence the word was used (1861) to describe the warm gray color of the Southern army uniforms in the American Civil War.
buttery (adj.): "resembling butter," late 14c., from butter (n.) + -y (2). Related: Butteriness.
buttery (n.): "place for storing liquor," originally "room where provisions are laid up" (late 14c.), from Old French boterie, from Late Latin botaria, from bota, variant of butta "cask, bottle;" see butt (n.2) + -ery.
butthead (n.): also butt-head, late 1980s, student slang, "objectionable person," from butt (n.1) + head (n.); perhaps influenced by butterhead, 1960s black slang for one who is a disgrace to the community. Earlier, butthead meant simply "the butt end, bottom" of anything (1630s).
butthole (n.): also butt-hole, "anus," 1950s slang, from butt (n.1) + hole (n.). Earlier it meant "blind hole; cul-de-sac" (early 20c.).
buttinski (n.): a jocular name for one who cuts into a line, etc., 1902, American English, from verbal phrase butt in (see butt (v.)) + surname ending based on Eastern European names.
buttock (n.): late 13c., singular of buttocks (q.v.).
buttocks (n.): late 13c., probably related to Old English buttuc "end, short piece of land" (see butt (n.1)).
button (n.): c.1300 (surname Botouner "button-maker" attested from mid-13c.), from Old French boton "a button," originally "a bud" (12c., Modern French bouton), from bouter, boter "to thrust," common Romanic (cf. Spanish boton, Italian bottone), ultimately from Germanic (see butt (v.)). Thus a button is, etymologically, something that pushes up, or thrusts out.

Meaning "point of the chin" is pugilistic slang, by 1921. A button as something you push to create an effect by closing an (electrical) circuit is attested from 1840s. Button-pusher as "deliberately annoying or provocative person" is attested by 1990 (in reference to Bill Gates, in "InfoWorld" magazine, Nov. 19). In the 1980s it meant "photographer."
button (v.): late 14c., "to furnish with buttons;" early 15c., "to fasten with buttons" (of a garment,) from button (n.) or from Old French botoner (Modern French boutonner), from boton (n.). Related: Buttoned; buttoning. Button-down (adj.) in reference to shirt collars is from 1916.
button-hole (n.): 1560s, from button (n.) + hole (n.). The verb, also buttonhole, meaning "to detain (someone) in conversation against his will" (1862) was earlier button-hold (1834), from button-holder (1806, in this sense). The image is of holding someone by the coat-button so as to detain him.
buttonwood (n.): also button-wood, "North American plane tree," 1690s, from button (n.) + wood (n.). So called for their characteristic round fruit.
buttress (n.): early 14c., from Old French (arc) botrez "flying buttress," apparently from bouter "to thrust against," of Frankish origin (cf. Old Norse bauta "to strike, beat"), from Proto-Germanic *butan, from PIE root *bhau- "to strike" (see butt (v.)).
buttress (v.): late 14c., literal and figurative, from buttress (n.). Related: Buttressed; buttressing.
butty (n.): "slice of bread and butter," 1855, northern English, from butter (n.) + -y (2).
butyl (n.): hydrocarbon radical, 1868, from butyric acid, a product of fermentation found in rancid butter, from Latin butyrum "butter" (see butter (n.)).
butyric (adj.): 1826, from stem of Latin butyrum "butter" (see butter (n.)) + -ic.
buxom (adj.): late 12c., buhsum "humble, obedient," from Proto-Germanic *buh- stem of Old English bugen "to bow" (see bow (v.)) + -som, for a total meaning "capable of being bent."

Meaning progressed from "compliant, obliging," through "lively, jolly," "healthily plump, vigorous," to (in women, and perhaps influenced by lusty) "plump, comely" (1580s). Used often of breasts, and by 1950s it had begun to be used more narrowly for "bosomy" and could be paired with slim (adj.). Dutch buigzaam, German biegsam "flexible, pliable" hew closer to the original sense of the English cognate.
buy (v.): Old English bycgan (past tense bohte) "to buy, pay for, acquire; redeem, ransom; procure; get done," from Proto-Germanic *bugjanan (cf. Old Saxon buggjan, Old Norse byggja, Gothic bugjan), of unknown origin, not found outside Germanic.

The surviving spelling is southwest England dialect; the word was generally pronounced in Old English and Middle English with a -dg- sound as "budge," or "bidge." Meaning "believe, accept as true" first recorded 1926. Related: Bought; buying. To buy time "prevent further deterioration but make no improvement" is attested from 1946.
buy (n.): "a purchase," especially a worthwhile one, 1879, American English, from buy (v.).
buy-in (v.): verbal phrase, "to purchase a commission or stock," 1826, from buy (v.) + in (adv.). As a noun by 1970.
buy-out (n.): also buy-out, "the purchasing of a controlling share in a company," 1976, from verbal phrase buy out "purchase someone's estate and turn him out of it," 1640s, from buy (v.) + out (adv.).
buyer (n.): c.1200, biggere "one who purchases," agent noun from buy (v.). Meaning "one whose job is to buy goods for a store" is from 1884. Buyer's market attested from 1886.
buzkashi (n.): Afghan sport, a sort of mounted polo played with a goat carcass, 1956, from Persian buz "goat" + kashi "dragging, drawing."
buzz (v.): late 15c., echoic of bees and other insects. Aviation sense of "fly low and close" is by 1941 (see buzz (n.)). Related: Buzzed; buzzing. Buzz off (1914) originally meant "to ring off on the telephone," from the use of buzzers to signal a call or message on old systems. As a command, it originally would have been telling someone to get off the line.
buzz (n.): "a busy rumour" [Rowe], 1620s (earlier "a fancy," c.1600), figurative use from buzz (v.). Literal sense of "humming sound" is from 1640s. A "buzz" was the characteristic sound of an airplane in early 20c.; hence verbal sense "to fly swiftly," by 1928; by 1940 especially in military use, "to fly low over a surface as a warning signal" (e.g. that target practice is about to begin):
The patrol aircraft shall employ the method of warning known as "buzzing" which consists of low flight by the airplane and repeated opening and closing of the throttle. [1941 Supplement to the Code of Federal Regulations of the United States of America," Chap. II, Corps of Engineers, War Department, p. 3434, etc. ]
Meaning "pleasant sense of intoxication" first recorded 1935. The children's game of counting off with 7 or multiples of it replaced by buzz is attested from 1864 and is mentioned in "Little Women" (1868). To give (someone) a buzz (by 1922) is from the buzz that announced a call on old telephone systems.
buzz-cut (n.): by 1973, American English, from buzz (n.), perhaps from the sound of the barber's electric clipper, + cut (n.) in the "haircut" sense.
buzz-saw (n.): 1858, American English, from buzz (v.) + saw (n.).