Online Etymology Dictionary

bacteriophage (n.): 1921, from French bactériophage (1917), from bacterio-, comb. form of bacteria, + -phage.
bacterium (n.): c. 1848, singular of bacteria (q.v.).
Bactrian: "inhabitant of Bactria," late 14c.; as a type of camel, c. 1600, from Latin Bactria, ancient region in what is now northwestern Afghanistan, literally "the western province," from Persian bakhtar "the west."
bad (adj.): c. 1200, "inferior in quality;" early 13c., "wicked, evil, vicious," a mystery word with no apparent relatives in other languages.* Possibly from Old English derogatory term bæddel and its diminutive bædling "effeminate man, hermaphrodite, pederast," probably related to bædan "to defile." A rare word before 1400, and evil was more common in this sense until c. 1700. Meaning "uncomfortable, sorry" is 1839, American English colloquial.

Comparable words in the other Indo-European languages tend to have grown from descriptions of specific qualities, such as "ugly," "defective," "weak," "faithless," "impudent," "crooked," "filthy" (such as Greek kakos, probably from the word for "excrement;" Russian plochoj, related to Old Church Slavonic plachu "wavering, timid;" Persian gast, Old Persian gasta-, related to gand "stench;" German schlecht, originally "level, straight, smooth," whence "simple, ordinary," then "bad").

Comparative and superlative forms badder, baddest were common 14c.-18c. and used as recently as Defoe (but not by Shakespeare), but yielded to comparative worse and superlative worst (which had belonged to evil and ill).

As a noun, late 14c., "evil, wickedness." In U.S. place names, sometimes translating native terms meaning "supernaturally dangerous." Ironic use as a word of approval is said to be at least since 1890s orally, originally in African-American vernacular, emerging in print 1928 in a jazz context. It might have emerged from the ambivalence of expressions like bad nigger, used as a term of reproach by whites, but among blacks sometimes representing one who stood up to injustice, but in the U.S. West bad man also had a certain ambivalence:
These are the men who do most of the killing in frontier communities, yet it is a noteworthy fact that the men who are killed generally deserve their fate. [Farmer & Henley]
*Farsi has bad in more or less the same sense as the English word, but this is regarded by linguists as a coincidence. The forms of the words diverge as they are traced back in time (Farsi bad comes from Middle Persian vat), and such accidental convergences exist across many languages, given the vast number of words in each and the limited range of sounds humans can make to signify them. Among other coincidental matches with English are Korean mani "many," Chinese pei "pay," Nahuatl (Aztecan) huel "well," Maya hol "hole."
bad-mouth (v.): "abuse someone verbally," 1941, probably ultimately from noun phrase bad mouth (1835), in African-American vernacular, "a curse, spell," translating an idiom found in African and West Indian languages. Related: Bad-mouthed; bad-mouthing.
badass (n.): "tough guy," 1950s U.S. slang, from bad + ass (n.2).
badder (adj.): obsolete or colloquial comparative of bad, common 14c.-18c.
baddest (adj.): obsolete or colloquial superlative of bad, common 14c.-18c.
baddish (adj.): "rather bad," 1755, from bad + -ish.
baddy (n.): "bad man," 1937, from bad + -y (3).
bade: Old English bæd, past tense of bid (v.).
badge (n.): mid-14c., perhaps from Anglo-French bage or from Anglo-Latin bagis, plural of bagia "emblem," all of unknown origin.
badger (n.): 1520s, perhaps from bage "badge" (see badge) + -ard "one who carries some action or possesses some quality," suffix related to Middle High German -hart "bold" (see -ard). If so, the central notion is the badge-like white blaze on the animal's forehead (as in French blaireau "badger," from Old French blarel, from bler "marked with a white spot;" also obsolete Middle English bauson "badger," from Old French bauzan, literally "black-and-white spotted"). But blaze (n.2) was the usual word for this.

An Old English name for the creature was the Celtic borrowing brock; also græg (Middle English grei, grey). In American English, the nickname of inhabitants or natives of Wisconsin (1833).
badger (v.): 1790, from badger (n.), based on the behavior of the dogs in the medieval sport of badger-baiting, still practiced in 18c. England. Related: Badgered; badgering.
badinage (n.): "light railery," 1650s, from French badinage "playfulness, jesting," from badiner (v.) "to jest, joke," from badin "silly, jesting," from Old Provençal badar "to yawn, gape," from Late Latin badare "to gape," from *bat-, the root of abash.
badlands (n.): "arid, highly eroded regions of the western U.S.," 1852, from bad + land (n.). Applied to urban districts of crime and vice since 1892 (originally with reference to Chicago).
badly (adv.): c. 1300, "unluckily;" late 14c., "wickedly, evilly; poorly, inadequately," from bad + -ly (2).
badminton (n.): 1874, from Badminton House, name of Gloucestershire estate of the Duke of Beaufort, where the game first was played in England, mid-19c., having been picked up by British officers from Indian poona. The place name is Old English Badimyncgtun (972), "estate of (a man called) Baduhelm."
badness (n.): late 14c., baddenesse; see bad + -ness.
Baedeker: "travel guide," 1863, from German printer and bookseller Karl Baedeker (1801-1859) whose popular travel guides began the custom of rating places with one to four stars. The Baedeker raids by the Luftwaffe in April and May 1942 targeted British cultural and historical sites.
baffle (v.): 1540s, "to disgrace," perhaps a Scottish respelling of bauchle "to disgrace publicly" (especially a perjured knight), which is probably related to French bafouer "to abuse, hoodwink" (16c.), possibly from baf, a natural sound of disgust, like bah (compare German baff machen "to flabbergast"). Meaning "to bewilder, confuse" is from 1640s; that of "to defeat someone's efforts" is from 1670s. Related: Baffled; baffling.
baffle (n.): "shielding device," 1881, from baffle (v.).
bafflement (n.): 1841, from baffle (v.) + -ment.
baffling (adj.): 1783, "bewildering," present participle adjective from baffle (v.); earlier a sailor's adjective for winds that blow variously and make headway difficult (c. 1770s).
bag (n.): c. 1200, bagge, from Old Norse baggi or a similar Scandinavian source; not found in other Germanic languages, perhaps ultimately of Celtic origin. Disparaging slang for "woman" dates from 1924 (though various specialized senses of this are much older). Meaning "person's area of interest or expertise" is 1964, from African-American vernacular, from jazz sense of "category," probably via notion of putting something in a bag.

To be left holding the bag (and presumably nothing else), "cheated, swindled" is attested by 1793. Many figurative senses, such as the verb meaning "to kill game" (1814) and its colloquial extension to "catch, seize, steal" (1818) are from the notion of the game bag (late 15c.) into which the product of the hunt was placed. To let the cat out of the bag "reveal the secret" is from 1760.
bag (v.): mid-15c., "to swell out like a bag;" also "to put money in a bag," from bag (n.). Earliest verbal sense was "to be pregnant" (c. 1400). Of clothes, "to hang loosely," 1824. For sense "catch, seize, steal," see bag (n.). Related: Bagged; bagging.
bag-end (n.): "bottom of a bag," c. 1400, from bag (n.) + end (n.).
bagatelle (n.): 1630s, "a trifle," from French bagatelle "knick-knack, bauble, trinket" (16c.), from Italian bagatella "a trifle," diminutive of Latin baca "berry." As "a piece of light music," it is attested from 1827.
bagel (n.): 1919, from Yiddish beygl, from Middle High German boug- "ring, bracelet," from Old High German boug "a ring," related to Old English beag "ring" (in poetry, an Anglo-Saxon lord was beaggifa "ring-giver"), from Proto-Germanic *baugaz, from PIE root *bheug- (3) "to bend," with derivatives referring to bent, pliable, or curved objects (such as Old High German biogan "to bend;" see bow (v.)).
bagful (n.): c. 1300, bagge-ful, from bag (n.) + -ful.
baggage (n.): mid-15c., "portable equipment of an army; plunder, loot," from Old French bagage "baggage, (military) equipment" (14c.), from bague "pack, bundle, sack," ultimately from the same Scandinavian source that yielded bag (n.). Baggage-smasher (1851) was American English slang for "railway porter."
bagger (n.): mid-15c., "retailer in grain" (as a surname from mid-13c., probably "maker of bags"), also, 1740, "miser;" agent noun from bag (v.). Of persons who bag various things for a living, from 19c.; meaning "machine that puts things in bags" is from 1896.
baggy (adj.): "puffed out, hanging loosely," 1831, from bag (n.) + -y (2). Bagging in this sense is from 1590s. Baggie as a small protective plastic bag is from 1969. Baggies "baggy shorts" is from 1962, surfer slang. Related: Baggily; bagginess.
Baghdad: a pre-Islamic name apparently of Indo-European origin and probably meaning "gift of god," with the first element related to Russian bog "god" and the second to English donor. Marco Polo (13c.) wrote it Baudac.
bagpipe (n.): late 14c., from bag (n.) + pipe (n.1); originally a favorite instrument in England as well as the Celtic lands, but by 1912 English army officers' slang for it was agony bags. Related: Bagpiper (early 14c.).
baguette (n.): 1727, a type of architectural ornament, from French baguette (16c.), from Italian bacchetta, literally "a small rod," diminutive of bacchio "rod," from Latin baculum "a stick" (see bacillus). Meaning "a diamond cut long" is from 1926; that of "a long, thin loaf of French bread" is from 1958.
bah: exclamation of contempt, 1817, perhaps c. 1600, probably from French bah, Old French ba, expressing surprise, scorn, dismay. Perhaps simply a natural exclamation in such situations; compare Greek babai!, an exclamation of surprise.
Baha'i: 1889, mystical, tolerant Iranian religion founded by a Mirza Ali Mohammed ibn Radhik, Shiraz merchant executed for heresy in 1850, and named for his leading disciple, Baha Allah (Persian "splendor of God;" ultimately from Arabic). It also is sometimes called Babism, after the name taken by the founder, Bab-ed-Din, "gate of the faith."
Bahamas: islands discovered by Columbus in 1492, settled by English in 1648, long after the native population had been wiped out by disease or carried off into slavery; the name is said to be from Spanish baja mar "low sea," in reference to the shallow water here, but more likely represents a local name, Guanahani, whose origin had been lost and whose meaning has been forgotten.
bail (n.1): "bond money," late 15c., a sense that apparently developed from that of "temporary release from jail" (into the custody of another, who gives security), recorded from early 15c. That evolved from earlier meaning "captivity, custody" (early 14c.). From Old French baillier "to control, to guard, deliver" (12c.), from Latin bajulare "to bear a burden," from bajulus "porter," which is of unknown origin. In late 18c. criminal slang, to give leg bail meant "to run away."
bail (v.1): "to dip water out of," 1610s, from baile (n.) "small wooden bucket" (mid-14c.), from nautical Old French baille "bucket, pail," from Medieval Latin *bajula (aquae), literally "porter of water," from Latin bajulare "to bear a burden" (see bail (n.1)). To bail out "leave suddenly" (intransitive) is recorded from 1930, originally of airplane pilots. Related: Bailed; bailing.
bail (n.2): "horizontal piece of wood in a cricket wicket," c. 1742, originally "any cross bar" (1570s), probably identical with Middle French bail "horizontal piece of wood affixed on two stakes," and with English bail "palisade wall, outer wall of a castle" (see bailey).
bail (v.2): "to procure someone's release from prison" (by posting bail), 1580s, from bail (n.1); usually with out. Related: Bailed; bailing.
bailey (n.): "wall enclosing an outer court," early 14c. (c. 1200 in Anglo-Latin), baylle, variant of bail, from Old French bail "stake, palisade, brace," which is of unknown origin, perhaps ultimately connected to Latin bacula "sticks," on notion of "stakes, palisade fence." Old Bailey, seat of Central Criminal Court in London, was so called because it stood within the ancient bailey of the city wall. The surname Bailey usually is from Old French bailli, a later form of baillif (see bailiff).
bailiff (n.): mid-13c., from Old French baillif (12c., nominative baillis) "administrative official, deputy," from Vulgar Latin *bajulivus "official in charge of a castle," from Latin bajulus "porter," which is of unknown origin. Used in Middle English of a public administrator of a district, a chief officer of a Hundred, or an officer under a sheriff.
bailiwick (n.): "district of a bailiff," early 15c., baillifwik, from bailiff (q.v.) + Middle English form of Old English wic "village" (see wick (n.2)). Figurative sense of "one's natural or proper sphere" is first recorded 1843.
bailout (n.): 1945, in aviation, from bail (v.) + out (adv.). As "federal help for private business in trouble," from 1968.
bain-marie (n.): 1822, from French bain-marie, from Medieval Latin balneum Mariae, literally "bath of Mary." According to French sources, perhaps so called for the gentleness of its heating. Middle English had balne of mary (late 15c.). French bain is from baigner "to bathe," from Latin balneare.
bairn (n.): "child" (of any age), Old English bearn "child, son, descendant," probably related to beran ("to bear, carry, give birth;" see bear (v.)). Originally not chiefly Scottish, but felt as such from c. 1700. This was the English form of the original Germanic word for "child" (see child). Dutch, Old High German kind, German Kind are from a prehistoric *gen-to-m "born," from the same root as Latin gignere. Middle English had bairn-team "brood of children."
bait (n.): "food put on a hook or trap to lure prey," c. 1300, from Old Norse beita "food," related to Old Norse beit "pasture," Old English bat "food," literally "to cause to bite" (see bait (v.)). Figurative sense "anything used as a lure" is from c. 1400.