Online Etymology Dictionary

brush (n.1): "dust-sweeper, a brush for sweeping," late 14c., also, c. 1400, "brushwood, brushes;" from Old French broisse (Modern French brosse) "a brush" (13c.), perhaps from Vulgar Latin *bruscia "a bunch of new shoots" (used to sweep away dust), perhaps from Proto-Germanic *bruskaz "underbrush."
brush (n.2): "shrubbery," early 14c., from Anglo-French bruce "brushwood," Old North French broche, Old French broce "bush, thicket, undergrowth" (12c., Modern French brosse), from Gallo-Roman *brocia, perhaps from *brucus "heather," or possibly from the same source as brush (n.1).
brush (v.1): late 15c., "to clean or rub (clothing) with a brush," also (mid-15c.) "to beat with a brush," from brush (n.1). Related: Brushed; brushing. To brush off someone or something, "rebuff, dismiss," is from 1941.
brush (v.2): "move briskly" especially past or against something or someone, 1670s, from earlier sense (c. 1400) "to hasten, rush," probably from brush (n.2), on the notion of a horse, etc., passing through dense undergrowth (compare Old French brosser "travel (through woods)," and Middle English noun brush "charge, onslaught, encounter," mid-14c.), but brush (n.1) probably has contributed something to it as well. Related: Brushed; brushing.
brushfire (n.): 1850, from brush (n.2) + fire (n.).
brusque (adj.): 1650s, from French brusque "lively, fierce," from Italian adjective brusco "sharp, tart, rough," perhaps from Vulgar Latin *bruscum "butcher's broom plant."
Brussels: capital of old Brabant, now of Belgium, of Germanic origin, from brocca "marsh" + sali "room, building," from Latin cella (see cell). It arose 6c. as a fortress on an island in a river. As a type of carpet, from 1799; as a type of lace, from 1748. Brussels sprouts (Brassica oleracea gemmifera) attested from 1748 (first written description is from 1580s).
brut (adj.): "dry," 1891, used of wines, especially champagnes, from French brut (14c.), literally "raw, crude" (see brute).
brutal (adj.): mid-15c., in reference to the nature of animals, from Latin brutus (see brute (adj.)) + -al (1). Of persons, "fierce," 1640s. Related: Brutally.
brutality (n.): 1630s, "savage cruelty, inhuman behavior," from brutal + -ity. Literal sense "condition or state of a brute" is from 1711.
brute (adj.): early 15c., "of or belonging to animals," from Middle French brut "coarse, brutal, raw, crude," from Latin brutus "heavy, dull, stupid," an Oscan word, from PIE root *gwere- (2) "heavy" (see grave (adj.)). Before reaching English the meaning expanded to "of the lower animals." Used of human beings from 1530s.
brute (n.): 1610s, from brute (adj.).
brutish (adj.): 1530s, "pertaining to animals," from brute (n.) + -ish. In reference to human brutes, from 1550s. Related: Brutishly; brutishness.
Brutus: A surname of the Junian gens. Association with betrayal traces to Marcus Junius Brutus (c. 85 B.C.E.-42 B.C.E.), Roman statesman and general and conspirator against Caesar.
bruxism (n.): "grinding the teeth unconsciously," from Greek ebryxa, aorist root of brykein "to gnash the teeth."
bryo-: word-forming element meaning "moss" in scientific compounds, from Greek bryos, bryon "moss."
bryophyte (n.): from Modern Latin Bryophyta (1864), from bryo- "moss" + -phyte "plant" (n.).
Brythonic (adj.): "of the Britons, Welsh," 1884, from Welsh Brython, cognate with Latin Britto (see Briton). Introduced by Welsh Celtic scholar Professor John Rhys (1840-1915) to avoid the confusion of using Briton/British with reference to ancient peoples, religions, and languages.
BS (n.): c. 1900, slang abbreviation of bullshit (q.v.).
btw: Internet abbreviation of by the way, in use by 1989.
bub (n.): familiar address for males, 1839, perhaps a variation of bud "a little boy" (1848), American English colloquial; perhaps from German bube "boy," or from English brother.
bubba (n.): Southern U.S. slang, 1860s, a corruption of brother.
bubble (n.): early 14c., perhaps from Middle Dutch bobbel (n.) and/or Middle Low German bubbeln (v.), all probably of echoic origin. Bubble bath first recorded 1949. Of financial schemes originally in South Sea Bubble (1590s), on notion of "fragile and insubstantial."
bubble (v.): mid-15c., perhaps from bubble (n.) and/or from Middle Low German bubbeln (v.), probably of echoic origin. Related: Bubbled; bubbling.
bubble-gum (n.): 1937, from bubble (n.) + gum (n.). Figurative of young teenager tastes or culture from the early 1960s.
bubbly (adj.): 1590s, from bubble (n.) + -ly (2). Of persons, from 1939. The slang noun meaning "champagne" (1920) is short for bubbly water (1910).
bubo (n.): late 14c., plural buboes, from Late Latin bubo (genitive bubonis) "swelling of lymph glands" (in the groin), from Greek boubon "the groin, swelling in the groin."
bubonic (adj.): "characterized by swelling in the groin," by 1795, from Latin bubo (genitive bubonis) "swelling of lymph glands" (in the groin), from Greek boubon "the groin; swelling in the groin" + -ic. Bubonic plague attested by 1827.
buccal (adj.): "pertaining to the cheek," 1831, from Latin bucca "cheek," especially when puffed out (later "mouth"); see bouche.
buccaneer (n.): 1660s, from French boucanier "user of a boucan," a native grill for roasting meat, from Tupi mukem (rendered in Portuguese as moquem c. 1587): "initial b and m are interchangeable in the Tupi language" [Klein]. For Haitian variant barbacoa, see barbecue. Originally used of French settlers working as hunters and woodsmen in the Spanish West Indies, a lawless and piratical set after they were driven from their trade by Spanish authorities in the 1690s.
Bucephalus: Alexander the Great's favorite horse, from Greek Boukephalos, literally "Ox-head," from bous "ox" (see cow (n.)) + kephale "head" (see cephalo-).
Men called [him] Bucephalus ... of the marke or brand of a buls head, which was imprinted vpon his shoulder. [Pliny, I.220, tr. Holland, 1601]
buck (n.1): "male deer," c. 1300, earlier "male goat;" from Old English bucca "male goat," from Proto-Germanic *bukkon (source also of Old Saxon buck, Middle Dutch boc, Dutch bok, Old High German boc, German Bock, Old Norse bokkr), perhaps from a PIE root *bhugo (source also of Avestan buza "buck, goat," Armenian buc "lamb"), but some speculate that it is from a lost pre-Germanic language. Barnhart says Old English buc "male deer," listed in some sources, is a "ghost word or scribal error."

Meaning "dollar" is 1856, American English, perhaps an abbreviation of buckskin, a unit of trade among Indians and Europeans in frontier days, attested in this sense from 1748. Pass the buck is first recorded in the literal sense 1865, American English:
The 'buck' is any inanimate object, usually knife or pencil, which is thrown into a jack pot and temporarily taken by the winner of the pot. Whenever the deal reaches the holder of the 'buck', a new jack pot must be made. [J.W. Keller, "Draw Poker," 1887]
Perhaps originally especially a buck-handled knife. The figurative sense of "shift responsibility" is first recorded 1912. Buck private is recorded by 1870s, of uncertain signification.
buck (v.): 1848, apparently with a sense of "jump like a buck," from buck (n.1). Related: Bucked; bucking. Buck up "cheer up" is from 1844.
buck (n.2): "sawhorse," 1817, American English, apparently from Dutch bok "trestle."
buck-eye (n.): "American horse chestnut," 1763, said to be so called from resemblance of the nut to a stag's eye. See buck (n.1) + eye (n.). Meaning "native of Ohio" is attested since 1822.
buckaroo (n.): 1889, American English, from bakhara (1827), from Spanish vaquero "cowboy," from vaca "cow," from Latin vacca (see vaccination). Spelling altered by influence of buck (n.1).
buckboard (n.): 1839, "plank on wheels," from board (n.1) + buck "body of a cart or wagon" (1690s), perhaps representing a dialectal survival of Old English buc "belly, body, trunk" (see bucket). As a type of vehicle constructed this way, from 1874.
bucket (n.): mid-13c., from Anglo-French buquet "bucket, pail," from Old French buquet "bucket," which is from Frankish or some other Germanic source, or a diminutive of cognate Old English buc "pitcher, bulging vessel," originally "belly" (buckets were formerly of leather as well as wood), both from West Germanic *buh- (source also of Dutch buik, Old High German buh, German Bauch "belly"), possibly from a variant of PIE root *beu-, *bheu- "to grow, swell" (see bull (n.2)).

Kick the bucket "to die" (1785) perhaps is from unrelated Old French buquet "balance," a beam from which slaughtered animals were hung; perhaps reinforced by the notion of suicide by hanging after standing on an upturned bucket (but Farmer calls attention to bucket "a Norfolk term for a pulley").
Buckinghamshire: Old English Buccingahamscir, from Buccingahamme (early 10c.), "River-bend land of the family or followers of a man called Bucca."
buckish (adj.): "dandyish," 1782, from buck (n.1) in the slang sense + -ish. Related: Buckishly.
buckle (n.): "spiked metal ring for holding a belt, etc., c. 1300, bukel, from Old French bocle "boss (of a shield)," then "shield," then by further extension "buckle, metal ring," (12c., Modern French boucle), from Latin buccula "cheek strap of a helmet," in Late Latin "boss of a shield," diminutive of bucca "cheek" (see bouche).
Boucle in the middle ages had the double sense of a "shield's boss" and "a ring"; the last sense has alone survived, and it metaph. developed in the boucle de cheveux, ringlets. [Kitchin]
buckle (v.2): "distort, warp, bend out of shape" 1520s, bokelen "to arch the body," from Middle French boucler "to bulge," from Old French bocler "to bulge," from bocle "boss of a shield" (see buckle (n.)). Meaning "bend under strong pressure" is from 1590s (figurative from 1640s) . Related: Buckled; buckling.
buckle (v.1): late 14c., bokelen, "to fasten with a buckle," from buckle (n.). Related: Buckled; buckling. To buckle down "apply effort, settle down," (1874) is said to be a variant of knuckle down (see knuckle).
buckler (n.): "small, round shield used to ward off blows," c. 1300, from Old French bocler "boss (of a shield), shield, buckler" (12c., Modern French bouclier), from Latin *buccularius (adj.) "having a boss," from buccula (see buckle (n.)).
bucko (n.): term of address, originally (1883) nautical and with a sense of "swaggering, domineering fellow." Probably from buck (n.1) in the slang sense of "a blood or choice spirit."
There are in London divers lodges or societies of Bucks, formed in imitation of the Free Masons: one was held at the Rose, in Monkwell-street, about the year 1705. The president is styled the Grand Buck. ["Dictionary of the Vulgar Tongue," 1811]
buckra (n.): disparaging term among African-Americans for "white person," especially a poor one, 1790, apparently from an African language; compare mbakara "master" in Efik, a language of the Ibibio people of southern Nigeria.
buckram (n.): early 13c., from Old French boquerant "fine oriental cloth" (12c., Modern French bougran), probably (along with Spanish bucarán, Italian bucherame) from Bukhara, city in central Asia from which it was imported to Europe. Originally a name of a delicate, costly fabric, it later came to mean coarse linen used for lining. The -m in the English word may indicate Italian origin (compare Italian bucherame, 14c.).
buckshot (n.): coarse kind of shot used for deer and other large game, 1776, from buck (n.1) + shot (n.).
buckskin (n.): c. 1300, "skin of a buck," from buck (n.1) + skin (n.). Meaning "leather made from buckskin" was in use by 1804. The word was a nickname for Continental troops in the American Revolution.
bucktooth (n.): 1540s, from buck (n.1), perhaps on the notion of "kicking up," + tooth. In French, buck teeth are called dents à l'anglaise, literally "English teeth." Old English had twisel toð "with two protruding front teeth." Related: Buck-toothed.