Online Etymology Dictionary

B: second letter of the Latin alphabet, corresponding to Greek beta, Phoenician beth, literally "house." It "has nothing of that variety of pronunciation shown by most English letters" [Century Dictionary]. The Germanic "b" is said to represent a "bh" sound in Proto-Indo-European, which continued as "bh" in Sanskrit, became "ph" in Greek (brother/Greek phrater; bear (v.)/Greek pherein) and "f" in Latin (frater, ferre).

Often indicating "second in order." B-movie is by 1939, usually said to be so called from being the second, or supporting, film in a double feature. Some film industry sources say it was so called for being the second of the two films major studios generally made in a year, and the one cast with less headline talent and released with less promotion. And early usage varies with grade-B movie, suggesting a perceived association with quality. B-side of a gramophone single is by 1962 (flip-side is by 1949).

B-girl, abbreviation of bar girl, U.S. slang for a woman paid to encourage customers at a bar to buy her drinks, is by 1936.
b'hoy (n.): 1846, U.S. colloquial for "spirited lad, young spark," supposedly from the Irish pronunciation of boy.
B'nai B'rith (n.): Jewish fraternal organization founded in New York City in 1843, Hebrew, literally "Sons of the Covenant," from bene, construct state of banim, plural of ben "son," + brith "covenant."
B.B.C.: also BBC, 1923, abbreviation of British Broadcasting Company, continued after 1927 when it was replaced by British Broadcasting Corporation. BBC English as a type of standardized English recommended for announcers is recorded from 1928.
B.C.: abbreviation of Before Christ, in chronology, attested by 1823. The phrase itself, Before Christ, in dating, with exact years, is in use by 1660s.
B.C.E.: initialism (acronym) for "Before Common Era" or "Before Christian Era," 1881; see C.E. A secular alternative to B.C.
b.o. (n.): by c. 1950, an abbreviation of body odor; an advertisers' invention.
baa: imitative of the cry or bleat of a sheep, attested from 1580s as a noun and verb, but probably older, as baa is recorded before this as a name for a child's toy sheep. Compare Latin bee "sound made by a sheep" (Varro), balare "to bleat;" Greek blekhe "a bleating;" Catalan be "a sheep." Related: Baaed; baaing.
Baal: late 14c., Biblical, from Late Latin Baal, Greek Baal, from Hebrew Ba'al, literally "owner, master, lord," a title applied to any deity (including Jehovah; see Hosea ii.16), but later a name of a particular Semitic solar deity worshipped licentiously by the Phoenecians and Carthaginians; from ba'al "he took possession of," also "he married;" related to or derived from the Akkadian god-name Belu (source of Hebrew Bel), name of Marduk. Identical with the first element in Beelzebub and the second in Hannibal ("grace of Baal"), Hasdrubal ("help of Baal"). The name has been used figuratively in English for any "false god."
Baath: pan-Arab socialist party, founded by intellectuals in Syria in 1943, from Arabic ba't "resurrection, renaissance." Related: Baathist.
baba (n.): light kind of plum cake, 1827, from French baba (19c.), the word and the thing said by French dictionaries to be from Polish baba.
Babbitt (n.): "conventional, complacent, materialistic American businessman," 1923, from the name of the title character of Sinclair Lewis' novel (1922).
His name was George F. Babbitt. He was forty-six years old now, in April 1920, and he made nothing in particular, neither butter nor shoes nor poetry, but he was nimble in the selling of houses for more money than people could afford to pay. [Sinclair Lewis, "Babbitt," 1922]
Earlier the name was used in metallurgy (1857) in reference to a type of soft alloy (1875).
babble (v.): mid-13c., babeln "to prattle, utter words indistinctly, talk like a baby," akin to other Western European words for stammering and prattling (Swedish babbla, Old French babillier, etc.) attested from the same era (some of which probably were borrowed from others), all probably ultimately imitative of baby-talk (compare Latin babulus "babbler," Greek barbaros "non-Greek-speaking"). "No direct connexion with Babel can be traced; though association with that may have affected the senses" [OED]. Meaning "to talk excessively" is attested from c. 1500. Related: Babbled; babbler; babbling.
babble (n.): c. 1500, "idle talk," from babble (v.). In 16c., commonly in reduplicated form bibble-babble (1530s). Meaning "inarticulate speech" is from 1660s. Other nouns meaning "idle talk" included babblery (1530s), babblement (1640s).
babbling (n.): "muttering, foolish talk," c. 1400, verbal noun from babble (v.). Other nouns meaning "idle talk" included babblery (1530s), babblement (1640s). The adjective babblative "given to idle talk" is attested from 1580s. Related: Babblingly.
babe (n.): late 14c., "infant, young child of either sex," short for baban (early 13c.), which probably is imitative of baby talk (see babble (v.)). In many languages the word means "old woman" (compare Russian babushka "grandmother," from baba "peasant woman"), and it is also sometimes a child's variant of papa "father."
Crist crid in cradil, "moder, baba!" [John Audelay, c. 1426]
Now mostly superseded by its diminutive form baby. Used figuratively for "a childish person" from 1520s. Meaning "attractive young woman" is 1915, college slang (baby as "girl, young woman, girlfriend" is attested by 1839; see babe). Babe in arms is one so young it has to be carried; babe in the woods "an innocent among perils" is from 1795.
Babel: capital of Babylon, now a ruin near Hillah in Iraq, late 14c., from Late Latin, from Hebrew Babhel (Genesis xi), from Akkadian bab-ilu "Gate of God" (from bab "gate" + ilu "god"). The name is a translation of Sumerian Ka-dingir. Meaning "confused medley of sounds" (1520s) is from the biblical story of the Tower of Babel and the confusion of tongues (Genesis xi). The element bab figures in place-names in the Middle East, such as Bab-el-Mandeb, the strait at the mouth of the Red Sea.
babelicious (adj.): 1991, from babe in the "attractive young woman" sense + ending from delicious.
babify (v.): "make childish," 1862, from babe + -ify. Related: Babified.
Babism (n.): religious and social system founded in 19c. Persia, 1850; see Baha'i.
baboon (n.): type of old world ape, c. 1400, babewyn, earlier "a grotesque figure used in architecture or decoration" (early 14c.), from French babouin "baboon," from Old French baboin "ape," earlier "simpleton, dimwit, fool" (13c.), also "gaping figure (such as a gargoyle)," so perhaps from Old French baboue "grimacing;" or perhaps it is imitative of the ape's babbling speech-like cries. Also see -oon.

German Pavian "baboon" is from Dutch baviaan, from Middle Dutch baubijn, a borrowing of the Old French word. Century Dictionary says Arabic maimun probably is from the European words.
babouche (n.): also baboosh, 1690s, from French babouche, from Arabic babush, from Persian paposh "a slipper," from pa "foot" (related to Avestan pad-, from PIE root *ped- "foot") + posh "covering." Arabic, lacking a -p-, regularly converts -p- in foreign words to -b-.
babu (n.): also baboo, 1782, Anglo-Indian, "native clerk (originally in Bengal) who writes English," from Hindi babu, title of respect, perhaps originally "father."
In Bengal and elsewhere, among Anglo-Indians, it is often used with a slight savour of disparagement, as characterizing a superficially cultivated, but too often effeminate, Bengali. [Yule and Burnell, "Hobson-Jobson," 1886]
In reference to "the ornate and somewhat unidiomatic English of an Indian who has learnt the language principally from books" [OED] from 1878.
babushka (n.): type of head covering for women, 1938, from Russian babushka "grandmother."
baby (v.): "to treat like a baby," 1742, from baby (n.). Related: Babied; babying.
baby (n.): late 14c., babi, "infant of either sex," diminutive of babe (see babe) with -y (3). Meaning "childish adult person" is from c. 1600. Meaning "youngest of a group" is by 1897. As a term of endearment for one's lover it is attested perhaps as early as 1839, certainly by 1901 (OED writes, "the degree of slanginess in the nineteenth-century examples is not easily determinable"); its popularity perhaps boosted by baby vamp "a popular girl" (see vamp (n.2)), student slang from c. 1922.

Meaning "minute reflection of oneself seen in another's eyes" is from 1590s (compare pupil (n.2)). As an adjective by 1750. Baby food is from 1833. Baby blues for "blue eyes" recorded by 1892 (the phrase also was used for "postpartum depression" 1950s-60s). To empty the baby out with the bath (water) is attested by 1909 (in G.B. Shaw; compare German das Kind mit dem Bade ausschütten, attested from 17c.). A baby's breath was noted for sweet smell, which also was supposed to attract cats, hence baby's breath as the name of a type of flower, attested from 1897. French bébé (19c.) is from English.
baby boom (n.): coined 1941, from baby (n.) + boom (n.); derivative baby-boomer (member of the one that began in the U.S. in 1945) is recorded by 1974.
baby-farmer (n.): "one who cares for the infants of those unable or unwilling to do so themselves," 1868, from baby (n.) + farmer. Related: Baby-farm.
babyish (adj.): "like a baby, extremely childish," 1753, from baby (n.) + -ish. Earlier in same sense was babish (1530s). Related: Babyishness.
Babylon: mid-14c., representing the Greek rendition of Akkadian Bab-ilani "the gate of the gods," from bab "gate" + ilani, plural of ilu "god" (compare Babel). The Old Persian form, Babiru-, shows characteristic transformation of -l- to -r- in words assimilated from Semitic. Formerly also applied by Protestants to the Church in Rome, from the woman "arrayed in purple and scarlet" in Revelations xvii.5 ("And upon her forehead was a name written, Mystery, Babylon the Great, the mother of harlots and abominations of the earth").
Babylonian (n.): 1560s; see Babylon + -ian. From 1630s as an adjective. Earlier in the adjectival sense was Babylonical (1530s).
babysit (v.): also baby-sit, 1947, from baby (n.) + sit (v.); figurative use (often contemptuous) by 1968. Babysitting is from 1946.
babysitter (n.): also baby-sitter, 1914, from baby (n.) + agent noun from sit (v.). Short form sitter is attested from 1937.
Bacardi: 1921, name for a brand of West Indian rum produced by Compania Ron Bacardi, originally of Cuba.
baccalaureate (n.): 1620s, "university degree of a bachelor," from Modern Latin baccalaureatus, from baccalaureus "student with the first degree," alteration of Medieval Latin baccalarius "one who has attained the lowest degree in a university, advanced student lecturing under his master's supervision but not yet having personal licence" (altered by folk etymology or word-play, as if from bacca lauri "laurel berry," laurels being awarded for academic success).

The Medieval Latin word is of uncertain origin; perhaps ultimately from Latin baculum "staff" (see bacillus), which the young student might carry. Or it might be a re-Latinization of bachelor in its academic sense.

In modern U.S. usage, baccalaureate usually is short for baccalaureate sermon (1864), a religious farewell address to a graduating class at an American college, from the adjectival sense "pertaining to the university degree of bachelor."
baccarat (n.): card game, 1848, from French baccara (19c.), which is of unknown origin. Baccarat is the name of a town in France that was noted for glass-making.
Bacchae (n.): "female attendants of Bacchus," from Greek Bakkhai, plural of Bakkhe, from Bakkhos (see Bacchus).
Bacchanal: 1530s (n.), "riotous, drunken roistering;" 1540s (adj.) "pertaining to Bacchus," from Latin bacchanalis "having to do with Bacchus (q.v.). Meaning "characterized by intemperate drinking" is from 1711; meaning "one who indulges in drunken revels" is from 1812.
Bacchanalia (n.): "drunken revelry," 1630s, from the name of the Roman festival held in honor of Bacchus, from neuter plural of Latin bacchanalis "having to do with Bacchus" (q.v.); the festivals became so notorious for excess that they were forbidden by the Senate 186 B.C.E. A participant is a Bacchant (1690s), fem. Bacchante, from French. The plural of both is Bacchantes.
Bacchanalian (adj.): 1560s, "characterized by intemperate drinking;" see Bacchanalia + -an. From 1620s as "pertaining to Bacchanals." As a noun from 1610s, "participant in the Bacchanalia."
Bacchus: Greek god of wine and revelry, a later name of Dionysus, late 15c., from Latin Bacchus, from Greek Bakkhos, perhaps related to Latin bacca "berry, fruit of a tree or shrub" (see bay (n.4)), or from an Asian language. Perhaps originally a Thracian fertility god.
bach (n.): 1845, American English, clipped form of bachelor (n.). Also in colloquial American English use as a verb (1864, typically with it) meaning "to live as an unmarried man," especially "to do one's own cooking and cleaning." Related: Bached; baching.
bachelor (n.): c. 1300, "young man;" also "youthful knight, novice in arms," from Old French bacheler, bachelor, bachelier (11c.) "knight bachelor," a young squire in training for knighthood, also "young man; unmarried man," and a university title. Of uncertain origin; perhaps from Medieval Latin baccalarius "vassal farmer, adult serf without a landholding," one who helps or tends a baccalaria "field or land in the lord's demesne" (according to old French sources, perhaps from an alteration of vacca "a cow" and originally "grazing land" [Kitchin]). Or from Latin baculum "a stick," because the squire would practice with a staff, not a sword. "Perhaps several independent words have become confused in form" [Century Dictionary].

Meaning in English expanded early 14c. to "young unmarried man," late 14c. to "one who has taken the lowest degree in a university." Bachelor party as a pre-wedding ritual is from 1882.
bachelorette (n.): "unmarried woman," 1896, from bachelor with French ending -ette. Replaced earlier bachelor-girl (1888). The word appears to have been formed in English; Old French had bachelette "young girl" (15c.), also bachelle, bacelette, bachelote; Modern French is said to use bachelière only in the "student" sense.
Jessica. Thanks! Is Mr. Sparrow a bachelor?
Miss Cornelia. He is, and in all probability will remain one.
Jessica. I'm beginning to think there are pleasanter conditions in this world than being a bachelorette.
Miss Cornelia. Where did you ever pick up such a remarkable word? A bachelorette! What in the world is a bachelorette?
Jessica (smiling). You are.
["The Dummy," Alice Yates Grant," 1896]
bacilli (n.): plural of bacillus (q.v.).
bacillus (n.): 1877, medical Latin, from Late Latin bacillus "wand," literally "little staff," diminutive of baculum "a stick, staff, walking stick," from PIE *bak- "staff" (also source of Greek bakterion; see bacteria) + instrumentive suffix -culo. Introduced as a term in bacteriology 1853 by German botanist Ferdinand Cohn (1828-1898).
back (n.): Old English bæc "back," from Proto-Germanic *bakam (cognates: Old Saxon and Middle Dutch bak, Old Frisian bek), with no known connections outside Germanic. In other modern Germanic languages the cognates mostly have been ousted in this sense by words akin to Modern English ridge (such as Danish ryg, German Rücken).

Many Indo-European languages show signs of once having distinguished the horizontal back of an animal (or a mountain range) from the upright back of a human. In other cases, a modern word for "back" may come from a word related to "spine" (Italian schiena, Russian spina) or "shoulder, shoulder blade" (Spanish espalda, Polish plecy).

By synecdoche, "the whole body," especially with reference to clothing. Meaning "upright part of a chair" is from 1520s. To turn (one's) back on (someone or something) "ignore" is from early 14c. As a U.S. football position by 1876, so called from being behind the line of rushers; further distinguished according to relative position as quarterback, halfback, fullback. Behind (someone's) back "clandestinely" is from late 14c.

To know (something) like the back of one's hand, implying familiarity, is first attested 1893 in a dismissive speech made to a character in Robert Louis Stevenson's "Catriona":
If I durst speak to herself, you may be certain I would never dream of trusting it to you; because I know you like the back of my hand, and all your blustering talk is that much wind to me.
The story, a sequel to "Kidnapped," has a Scottish setting and context, and the back of my hand to you was noted in the late 19th century as a Scottish expression meaning "I will have nothing to do with you" [see Longmuir's edition of Jamieson's Scottish dictionary]. In English generally, the back of (one's) hand has been used to imply contempt and rejection since at least 1300. Perhaps the connection of a menacing dismissal is what made Stevenson choose that particular anatomical reference.
back (adj.): "being behind, away from the front, in a backward direction," Middle English, from back (n.) and back (adv.); often difficult to distinguish from these when the word is used in combinations. Formerly with comparative backer (c. 1400), also backermore. To be on the back burner in the figurative sense is from 1960, from the image of a cook keeping a pot there to simmer while at work on another concoction at the front of the stove.
back (adv.): "to or toward the rear or the original starting place; in the past; behind in position," literally or figuratively, late 14c., shortened from abak, from Old English on bæc "backwards, behind, aback" (see back (n.), and compare aback). Adverbial phrase back and forth attested from 1814.
back (v.): mid-15c., "to keep something back, hinder," from back (adv.). Meaning "cause to move back" is from 1781. Intransitive sense "move or go back" is from late 15c. Meaning "furnish with a back or backing" is from 1728, from back (n.). Meaning "to support" (as by a bet) is attested from 1540s. Related: Backed; backing.