Online Etymology Dictionary

bumbailiff (n.): server of writs, maker of arrests, etc., c.1600, from bum "arse" (see bum (n.1)), because he was always felt to be close behind, + bailiff.
bumble (v.): "to flounder, blunder," 1530s, probably of imitative origin. Related: Bumbled; bumbler; bumbling.
Bumble: "self-important petty official," 1856, from the name of the fussy, pompous, stupid beadle in Dickens' "Oliver Twist."
bumblebee (n.): also bumble-bee, 1520s, replacing Middle English humbul-be (altered by association with Middle English bombeln "to boom, buzz," late 14c.); echoic, from PIE echoic root *kem "to hum."
bumf (n.): "papers, paperwork," 1889, British schoolboy slang, originally "toilet-paper," from bum-fodder.
bummer (n.): "loafer, idle person," 1855, possibly an extension of the British word for "backside" (similar development took place in Scotland by 1540), but more probably from German slang bummler "loafer," agent noun from bummeln "go slowly, waste time."

According to Kluge, the German word is from 17c., and the earliest sense of it is "oscillate back and forth;" possibly connected to words in German for "dangle" (baumeln), via "back-and-forth motion" of a bell clapper, transferred to "going back and forth," hence "doing nothing." Meaning "bad experience" is 1968 slang.
bump (n.): 1590s, "protuberance caused by a blow;" 1610s as "a dull, solid blow;" see bump (v.). The dancer's bump and grind attested from 1940.
bump (v.): 1560s, "to bulge out;" 1610s, "to strike heavily," perhaps from Scandinavian, probably echoic, original sense was "hitting" then of "swelling from being hit." Also has a long association with obsolete bum "to make a booming noise," which perhaps influenced surviving senses such as bumper crop, for something full to the brim (see bumper). To bump into "meet" is from 1880s; to bump off "kill" is 1908 in underworld slang. Related: Bumped; bumping. Bumpsy (adj.) was old slang for "drunk" (1610s).
bumper (n.): 1670s, "glass filled to the brim;" perhaps from notion of bumping as "large," or from a related sense of "booming" (see bump (v.)). Meaning "anything unusually large" is from 1759, slang. Agent-noun meaning "buffer of a car" is from 1839, American English, originally in reference to railway cars; 1901 of automobiles (in phrase bumper-to-bumper, in reference to a hypothetical situation; of actual traffic jams by 1908).
bumpkin (n.): "awkward country fellow," 1560s, probably from Middle Dutch bommekijn "little barrel," diminutive of boom "tree" (see beam (n.)). Apparently, though itself Dutch, it began as a derogatory reference to Dutch people as short and dumpy.
bumptious (adj.): "assertive," 1803, probably a humorous coinage from bump on the pattern of fractious, etc. Related: Bumptiously; bumptiousness.
bumpy (adj.): 1865, from bump + -y (2).
Fasten your seatbelts. It's going to be a bumpy night. [Bette Davis ("Margo Channing"), "All About Eve," 1950]
Related: Bumpiness.
bun (n.): late 14c., origin obscure, perhaps from Old French buignete "a fritter," originally "boil, swelling," diminutive of buigne "swelling from a blow, bump on the head," from a Germanic source (cf. Middle High German bunge "clod, lump"), or from Gaulish *bunia (cf. Gaelic bonnach). Spanish buñelo "a fritter" apparently is from the same source. Of hair coiled at the back of the head, first attested 1894. To have a bun in the oven "be pregnant" is from 1951.

The first record of buns in the sense of "male buttocks" is from 1960s, perhaps from a perceived similarity; but bun also meant "tail of a hare" (1530s) in Scottish and northern England dialect and was transferred to human beings (and conveniently rhymed with nun in ribald ballads). This may be an entirely different word; OED points to Gaelic bun "stump, root."
buna (n.): synthetic rubber made from butadiene, from German Buna, from first elements of butadiene, name of a hydrocarbon (related to butane; the suffix indicates the presence of two double bonds) + Na, indicating sodium (from natrium; see sodium).
bunch (n.): early 14c., "protuberance on the body, swelling," perhaps echoic of the sound of hitting and connected to bump (cf., possibly in similar relationship, hump/hunch).

The sense of "cluster" is mid-15c.; connection with the earlier sense is obscure, and this may be a separate word, perhaps through a nasalized form of Old French bouge (2), 15c., from Flemish boudje diminutive of boud "bundle." Meaning "a lot, a group" is from 1620s.
bunch (v.): "to bulge out," late 14c., from bunch (n.). Meaning "to gather up in a bunch" (transitive) is from 1828; sense of "to crowd together" (intransitive) is from 1873. Related: Bunched; bunching.
buncombe (n.): see bunk (n.2).
bund (n.): "league, confederacy," 1850, from German Bund (related to English band (n.2) and bind (v.)). In names of various fraternal organizations, in U.S. especially the German-American Bund, pro-Nazi organization founded 1936.
Bundestag (n.): German federal council, 1879, from German Bundestag, from genitive of Bund "league, confederacy, association" (related to English band (n.2) and bind (v.)) + tag, literally "day;" as a verb, tagen, meaning "to sit in conference" (see day; also cf. adjourn). Hence also Bundesrat, from rat, rath "council" (see read (v.)).
bundle (n.): early 14c., "bound collection of things," from Middle Dutch bondel, diminutive of bond, from binden "to bind," or perhaps a merger of this word and Old English byndele "binding," from Proto-Germanic *bundilin (cf. German bündel "to bundle"), from PIE root *bhendh- "tie" (see bend (v.)). Meaning "a lot of money" is from 1899. To be a bundle of nerves "very anxious" is from 1938.
bundle (v.): 1620s, "to make into a bundle," from bundle (n.); meaning "to wrap up in warm heavy clothes" is from 1893. Meaning "to sleep with another, clothed, in the same bed," a noted former custom in New England, is from 1781. Meaning "to send away hurriedly" is from 1823. Related: Bundled; bundling.
bundling (n.): 1640s, "a gathering into a bundle," verbal noun from bundle (v.). Meaning "sharing a bed for the night, fully dressed, wrapped up with someone of the opposite sex" (1782) is a former local custom in New England (especially Connecticut and southeastern Massachusetts). It was noted there from about 1750s and often regarded by outsiders as grossly immoral, but New Englanders wrote defenses of it and claimed it was practiced elsewhere, too. It seems to have died out with the 18th century.
I am no advocate for temptation; yet must say, that bundling has prevailed 160 years in New England, and, I verily believe, with ten times more chastity than the sitting on a sofa. I had daughters, and speak from near forty years' experience. Bundling takes place only in cold seasons of the year--the sofa in summer is more dangerous than the bed in winter. [The Rev. Samuel Peters, "A general history of Connecticut," 1782]
bung (n.): mid-15c., "large stopper for a cask," from Middle Dutch bonge "stopper;" or perhaps from French bonde "bung, bunghole" (15c.), which may be of Germanic origin (or the Germanic words may be borrowed from Romanic), or it may be from Gaulish *bunda (cf. Old Irish bonn, Gaelic bonn, Welsh bon "base, sole of the foot"). It is possible that either or both of these sources is ultimately from Latin puncta in the sense of "hole." Transferred to the cask-mouth itself (also bung-hole) from 1570s.
bung-hole (n.): also bunghole, "hole in a cask for a stopper," 1570s, from bung (n.) + hole (n.). Sense extended to "anus" by c.1600.
bungalow (n.): 1670s, from Gujarati bangalo, from Hindi bangla "low, thatched house," literally "Bengalese," used elliptically for "house in the Bengal style" (see Bengal). Related: Bungaloid.
bungee (n.): 1930, "elastic rope;" used in late 19c. British schoolboy slang for "rubber eraser;" probably from notions of bouncy and spongy; first record of bungee jumping is from 1979.
bungle (v.): 1520s, origin obscure. OED suggests imitative; perhaps a mix of boggle and bumble, or more likely from a Scandinavian word akin to Swedish bangla "to work ineffectually," Old Swedish bunga "to strike" (cf. German Bengel "cudgel," also "rude fellow"). Related: Bungled; bungling.
bungle (n.): 1650s, from bungle (v.).
bungler (n.): 1530s, agent noun from bungle (v.).
bungling (n.): 1660s, verbal noun from bungle (v.).
bungling (adj.): 1580s, past participle adjective from bungle (v.). Related: Bunglingly.
bunion (n.): 1718, apparently from East Anglian dialectic bunny "lump, swelling" (16c.), which is probably from Middle French buigne "bump on the head, swelling from a blow" (see bun).
bunk (n.1): "sleeping berth," 1758, probably a shortened form of bunker (n.) in its sense "seat." Bunk-bed (n.) attested by 1869.
bunk (n.2): "nonsense," 1900, short for bunkum, phonetic spelling of Buncombe, a county in North Carolina. The usual story (by 1841) of its origin is this: At the close of the protracted Missouri statehood debates, supposedly on Feb. 25, 1820, N.C. Representative Felix Walker (1753-1828) began what promised to be a "long, dull, irrelevant speech," and he resisted calls to cut it short by saying he was bound to say something that could appear in the newspapers in the home district and prove he was on the job. "I shall not be speaking to the House," he confessed, "but to Buncombe." Bunkum has been American English slang for "nonsense" since 1841 (from 1838 as generic for "a U.S. Representative's home district").
MR. WALKER, of North Carolina, rose then to address the Committee on the question [of Missouri statehood]; but the question was called for so clamorously and so perseveringly that Mr. W. could proceed no farther than to move that the committee rise. [Annals of Congress, House of Representatives, 16th Congress, 1st Session, p. 1539]
bunk (v.): "to sleep in a bunk," 1840, originally nautical, from bunk (n.1). Related: Bunked; bunking.
bunker (n.): 1758, originally Scottish, "seat, bench," of uncertain origin, possibly a variant of banker "bench" (1670s; see bank (n.2)); possibly from a Scandinavian source (cf. Old Swedish bunke "boards used to protect the cargo of a ship"). Of golf courses, first recorded 1824, from extended sense "earthen seat" (1805); meaning "dug-out fortification" probably is from World War I.
Bunker Hill: battle site in Massachusetts, U.S., was land assigned in 1634 to George Bunker, who came from the vicinity of Bedford, England. The name dates from 1229, as Bonquer and is from Old French bon quer "good heart."
bunkum (n.): variant of Buncombe.
bunny (n.): 1680s, diminutive of Scottish dialectal bun, pet name for "rabbit," previously (1580s) for "squirrel," and also a term of endearment for a young attractive woman or child (c.1600). Ultimately it could be from Scottish bun "tail of a hare" (1530s), or from French bon, or from a Scandinavian source. The Playboy Club hostess sense is from 1960. The Bunny Hug (1912), along with the foxtrot and the Wilson glide, were among the popular/scandalous dances of the ragtime era.
Bunsen burner: 1879, named for Prof. Robert Wilhelm Bunsen (1811-1899) of Heidelberg, who invented it in 1855. He also was co-inventor of the spectroscope.
bunt (v.): 1825, "to strike with the head or horns," perhaps an alteration of butt (v.) with a goat in mind, or a survival from from Middle English bounten "to return." As a baseball term from 1889. Related: Bunted; bunting.
bunt (n.): 1767, "a push;" see bunt (v.). Baseball sense is from 1889.
bunting (n.1): "flag material," 1742, perhaps from Middle English bonting gerundive of bonten "to sift," because cloth was used for sifting grain, via Old French, from Vulgar Latin *bonitare "to make good."
bunting (n.2): lark-like bird, c.1300, bountyng, of unknown origin. Perhaps from buntin "plump" (cf. baby bunting, also Scots buntin "short and thick;" Welsh bontin "rump," and bontinog "big-assed"), or a double diminutive of French bon. Or it might be named in reference to speckled plumage and be from an unrecorded Old English word akin to German bunt "speckled," Dutch bont.
bunyip (n.): 1848, fabulous swamp-dwelling animal (supposedly inspired by fossil bones), from an Australian aborigine language.
buoy (n.): late 13c., perhaps from either Old French buie or Middle Dutch boeye, both from West Germanic *baukna "beacon, signal" (see beacon). OED, however, supports Middle Dutch boeie, or Old French boie "fetter, chain" (see boy), "because of its being fettered to a spot."
buoy (v.): late 16c., "to mark with a buoy," from buoy (n.). Meaning "rise up, lift, sustain" is from c.1600, perhaps influenced by Spanish boyar "to float," ultimately from the same source. In the figurative sense (of hopes, spirits, etc.) it is recorded from 1640s. Related: Buoyed; buoying.
buoyance (n.): 1821, from buoyant + -ance.
buoyancy (n.): 1713, from buoyant + -cy. Figurative sense (of spirits, etc.) is from 1819.
buoyant (adj.): 1570s, perhaps from Spanish boyante, present participle of boyar "to float," from boya "buoy," from Dutch boei (see buoy (n.)). Of personalities, etc., from c.1748. Related: Buoyantly.