Online Etymology Dictionary

B movie: 1930s, usually said to be so called from being the second, or supporting, film in a double feature. But 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 made with less headline talent and released with less promotion.
b'hoy: 1846, U.S. colloquial for "spirited lad, young spark," supposedly from the Irish pronunciation of boy.
B'nai B'rith: Jewish fraternal organization founded in New York City in 1843, from Heb., lit. "Sons of the Covenant," from bene, state construct of banim, pl. of ben "son" + brith "covenant."
B-girl: 1936, abbreviation of bar girl, U.S. slang for a woman paid to encourage customers at a bar to buy her drinks.
B.B.C.: acronym for British Broadcasting Corporation, established 1927 replacing British Broadcasting Company, so the acronym itself dates to 1923. BBC English as a type of standardized English recommended for announcers is recorded from 1928.
B.C.E.: acronym for "Before Common Era" or "Before Christian Era," 1881; see C.E. A secular alternative to B.C.
b.o.: abbreviation of body odor, by c.1950; an advertisers' invention.
baa: imitative sound of a sheep, attested from 1580s, but probably older as baa is recorded before this a name for a child's toy sheep.
Baal: "The name of many deities of the Semitic peoples" [Klein], late 14c., Biblical use is from Heb. Ba'al, lit. "owner, master, lord," from ba'al "he took possession of," also "he married;" related to Akkad. Belu (source of Heb. Bel), name of Marduk. Also related to the first element in Beelzebub. Used figuratively for any "false god."
Baath: pan-Arab socialist party, founded by intellectuals in Syria in 1943, from Arabic ba't "resurrection, renaissance."
baba: kind of plum cake, 1827, from Fr. baba (19c.), said by French etymology dictionaries to be from Polish baba.
Babbitt: "conventional, complacent, materialistic American businessman," 1923, from George Babbitt, 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]
babble: early 13c., babeln "to prattle," akin to other Western European words for stammering and prattling (cf. Swedish babbla, O.Fr. babillier) attested from the same era, some of which probably were borrowed from others, but etymologists cannot now determine which were original. Probably imitative of baby-talk, in any case (cf. L. babulus "babbler," Gk. barbaros "non-Greek-speaking"). "No direct connexion with Babel can be traced; though association with that may have affected the senses" [OED]. Meaning "to repeat oneself incoherently, speak foolishly" is attested from early 15c. Related: Babbled; babbling.
babe: late 14c., short for baban (early 13c.), which probably is imitative of baby talk (cf. babble), however in many languages the cognate word means "old woman" (cf. Rus. babushka "grandmother," from baba "peasant woman"). Now mostly superseded by its dim. form baby. Used figuratively for "a childish person" from 1520s. Meaning "attractive young woman" is 1915, college slang; related babelicious first recorded 1991.
Babel: capital of Babylon, late 14c., from Heb. Babhel (Gen. ix), 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.
Babism: 1850; see Baha'i.
baboon: type of ape, c.1400, babewyn, earlier "a grotesque figure used in architecture or decoration" (early 14c.), from Fr. babouin "baboon," from O.Fr. baboin "ape," earlier "simpleton, dimwit, fool" (13c.), also "gaping figure (such as a gargoyle)," so perhaps from O.Fr. baboue "grimacing;" or perhaps it is imitative of the ape's babbling speech-like cries. Ger. Pavian "baboon" is from Du. baviaan, from M.Du. baubijn, a borrowing of the O.Fr. word.
babouche: 1690s, from Fr. babouche, from Arabic babush, from Pers. papush, from pa "foot" (related to Avestan pad-, see foot) + posh "covering." Arabic, lacking a -p-, regularly converts -p- in foreign words to -b-.
babushka: type of head covering for women, 1938, from Rus. babushka "grandmother."
baby: late 14c., babi, dim. of baban (see babe). The verb meaning "to treat like a baby" is from 1742. As a term of endearment for one's lover it is attested perhaps as early as 1839, certainly by 1901; its popularity perhaps boosted by baby vamp "a popular girl," student slang from c.1922. Baby blues for "blue eyes" recorded by 1944 (the phrase also was used for "postpartum depression" 1950s-60s). To empty the baby out with the bath (water) is first recorded 1909 in G.B. Shaw (cf. Ger. das Kind mit dem Bade ausschütten).
baby boom: coined 1941, from baby + boom; derivative baby-boomer (member of the one that began 1945) recorded by 1974.
Babylon: mid-14c., from Greek version of Akkad. Bab-ilani "the gate of the gods," from bab "gate" + ilani, pl. of ilu "god" (cf. Babel). The O.Pers. form, Babiru-, shows characteristic transformation of -l- to -r- in words assimilated from Semitic.
babysitter: 1937, also baby-sitter, from baby + agent noun of sit. Short form sitter is attested from 1943. The verb babysit (or baby-sit) is attested by 1947; fig. use (often contemptuous) by 1972. Babysitting also is from 1947.
Bacardi: 1921, name for a brand of West Indian rum produced by Compania Ron Bacardi, originally of Cuba.
baccalaureate: 1620s, "university degree of a bachelor," from M.L. baccalaureus "student with the first degree," altered by a play on words with bacca lauri "laurel berry" (laurels being awarded for academic success). The M.L. word perhaps ultimately is derived from L. baculum "staff" (see bacillus), which the young student might carry, but it is more likely just a re-Latinization of bachelor (q.v.) in its academic sense. In modern U.S. usage, the word usually is short for baccalaureate-sermon (1864), a religious farewell address to the graduating class.
baccarat: card game, 1866, from Fr. baccara (19c.), of unknown origin.
Bacchae: "female attendants of Bacchus," from Gk. Bakkhai, pl. of Bakkhe, from Bakkhos (see Bacchus).
bacchanal: 1530s, from L. bacchanalis "having to do with Bacchus" (see Bacchus). Meaning "riotous, drunken roistering; orgy" is from 1711.
bacchanalia: "drunken revelry," 1630s, from the name of the Roman festival held in honor of Bacchus, from L. neut. pl. of bacchanalis (see Bacchus). A participant is a Bacchant (1690s), fem. Bacchante, from French. Related: Bacchanalian (adj., 1620s).
Bacchus: Greek god of wine and revelry, late 15c., from L. Bacchus, from Gk. Bakkhos, perhaps related to L. bacca "berry, olive-berry, bead, pearl." Perhaps originally a Thracian fertility god.
bach: 1855, clipped form of bachelor (q.v.). Also in colloquial Amer.Eng. use as a verb (1870) meaning "to live as an unmarried man," esp. to do one's own cooking and cleaning.
bachelor: c.1300, "youthful knight, novice in arms," from O.Fr. bacheler (11c.) "knight bachelor," a young squire in training for knighthood, probably from M.L. baccalarius "vassal farmer," one who helps or tends a baccalaria "section of land." Or from L. baculum "a stick," since the squire would practice with a staff, not a sword. Meaning evolved 14c. from "knight in training" to "junior member of a guild or university" to "unmarried man" (late 14c.), an evolution that paralleled the word's development in French. Bachelor party is first recorded 1922.
bachelorette: 1935, from bachelor with Fr. ending -ette. Replaced earlier bachelor-girl (1895). M.Fr. had bachelette "young girl;" Mod.Fr. bachelière is found only in the "student" sense.
bacilli: pl. of bacillus (q.v.).
bacillus: 1883, from Mod.L., "little rod," from L.L. bacillus "wand," lit. "little staff," dim. of baculum "a stick," from PIE base *bak- "staff," also source of Gk. bakterion (see bacteria). Introduced as a term in bacteriology 1853 by Ger. botanist Ferdinand Cohn (1828-1898).
back (n.): O.E. bæc "back, backwards, behind," from P.Gmc. *bakam (cf. O.S., M.Du. bak, O.Fris. bek), with no known connections outside Germanic. The cognates mostly have been ousted in this sense in other modern Germanic languages by words akin to Modern English ridge (cf. Dan. ryg, Ger. Rücken). Many I.E. 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" (It. schiena, Rus. spina) or "shoulder, shoulder blade" (Sp. espalda, Pol. plecy).
back (v.): late 15c., "to move (something) back," from back (adj.); meaning "to support" (as by a bet) is first attested 1540s.
back (adj.): O.E. bæc "backwards, behind" (see back (n.)). Back-seat driver first attested 1926. The back of (one's) hand has been used to imply contempt and rejection since at least 1300; to know (something) like the back of one's hand, implying familiarity, is first attested 1893. 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 he or she works on another concoction at the front of the stove. Back-to-nature (adj.) is first attested 1915.
back down: in fig. sense of "withdraw a charge," 1859, Amer.Eng., from notion of descending a ladder, etc.; from back (v.) + down (adv.).
back off (v.): "retreat, stop annoying someone," by 1938, from back (v.) + off.
back up (v.): 1767, "stand behind and support," from back (v.) + up. The noun meaning "standby, reserve" is recorded from 1952 (often written as one word, backup); specific reference to computing is from 1965.
back-formation: coined c.1890s by Eng. lexicographer James Murray (1837-1915) from back (adj.) + noun of condition from form (q.v.).
back-talk: "impertinent retort," 1858, originally often used in literary attempts at low Irish idiom, from back (adj.) + talk.
backbencher: 1874 in the House of Commons sense, from back (adj.) + bench, occupants of the rear seats being the least-prominent politicians.
backbiting: late 12c., bacbitunge, from back (adj. or n.) + biting.
backbone: "spine," c.1300, from back (n.) + bone. Fig. sense of "strength of character" is attested from 1843.
backdate: 1946, from back (adj.) + date. Cf. antedate.
backdoor: "devious, shady, illegal," 1640s, from back + door. The notion is of business done out of public view. The association with sodomy is at least from 19c.; also back-door man "a married woman's lover," black slang, early 20c.
backdrop: 1913, in U.S. theatrical argot, from back + drop.
backfill (n.): 1901 (as backfilling), from back (adj.) + fill (n.). The verb was in use by 1930.