Online Etymology Dictionary

behaviorism (n.): coined 1913 by U.S. psychologist John B. Watson (1878-1958) from behavior + -ism. Behaviorist is from the same time.
behaviour (n.): chiefly British English spelling of behavior; for suffix, see -or.
behavioural (adj.): chiefly British English spelling of behavioral (q.v.); for spelling, see -or.
behead (v.): Old English beheafdian, from be-, here with privative force, + heafod (see head (n.)). Related: Beheaded; beheading.
beheld (v.): past tense and past participle of behold.
behemoth (n.): late 14c., huge biblical beast (Job xl:15), from Latin behemoth, from Hebrew b'hemoth, usually taken as plural of intensity of b'hemah "beast." But the Hebrew word is perhaps a folk etymology of Egyptian pehemau, literally "water-ox," the name for the hippopotamus.
Long before Jumbo was dreamed of, a hippo was exhibited by George K. Bailey, who invented the tank on wheels now used so generally in the circuses. The beast was advertised as "the blood sweating Behemoth of Holy Writ," and he made several men rich. [Isaac F. Marcosson, "Sawdust and Gold Dust," in "The Bookman," June 1910]
behest (n.): Old English behæs "a vow," perhaps from behatan "to promise" (from be- + hatan "command, call;" see cite) and confused with obsolete hest "command," which may account for the parasitic -t as well as the Middle English shift in meaning to "command, injunction" (late 12c.).
behind (adv.): Old English behindan "behind, after," from bi "by" + hindan "from behind" (see hind (adj.)). The prepositional sense emerged in Old English. Euphemistic noun meaning "backside of a person" is from 1786. Phrase behind the times is from 1905. Behind the scenes (1711) is from the theater; figurative sense attested by 1779.
behindhand (adv., adj.): 1520s, from behind + -hand, probably on model of beforehand.
behold (v.): Old English bihaldan (West Saxon behealdan) "give regard to, hold in view," also "to keep hold of, to belong to," from be- + haldan, healdan (see hold). Related: Beheld; beholding. A common West Germanic compound, cf. Old Saxon bihaldan "hold, keep," Old Frisian bihalda, Old High German bihaltan, German behalten, but "[t]he application to watching, looking, is confined to English" [OED].
beholden (adj.): "under obligation," mid-14c., originally past participle of behold (and preserving the original past participle of hold), but a sense directly related to this usage is not recorded among the many and varied meanings attested for behold.
beholder (n.): late 14c., agent noun from behold.
behoof (n.): c.1200, "use, benefit, advantage;" Old English had bihoflic "useful," implying *bihof "advantage, utility;" from Proto-Germanic *bi-hof "that which binds, requirement, obligation" (cf. Old Frisian bihof "advantage," Dutch behoef, Middle High German bihuof "useful thing," German Behuf "benefit, use, advantage"). In the common Germanic compound, the first element, likely intensive, is cognate with be- and the second with Old English hof, past tense of hebban "to raise" (see heave (v.)). The original sense is perhaps, then, "taking up (for oneself)."
behoove (v.): Old English behofian "to have need of, have use for," verbal form of the ancient compound word represented by behoof.
Historically, it rimes with move, prove, but being now mainly a literary word, it is generally made to rime with rove, grove, by those who know it only in books. [OED]
behove: chiefly British English spelling of behoove.
beige (n.): 1858, "fine woolen fabric," from dialectal French beige "yellowish-gray, brownish-gray," from Old French bege "the natural color of wool and cotton; raw, not dyed" (13c.), of obscure origin. "Das Wort lebt namentlich in der Bourgogne und Fr. Comté, daneben aber auch im Südwesten" [Gamillscheg]. As a shade of color, it is attested from 1879. As an adjective by 1879.
beignet (n.): "fritter," 1835, from French beignet "fritter, eggroll, doughnut" (14c.), from Old French buigne "bump, lump," from a Germanic source (cf. Middle High German bunge "clod, lump"), or from Gaulish *bunia (cf. Gaelic bonnach).
Beijing: Chinese capital, from bei "north" + jing "capital" (as opposed to Nanking, literally "southern capital").
being (n.): c.1300, "condition, state, circumstances; presence, fact of existing," early 14c., existence," from be + -ing. Sense of "that which physically exists, person or thing" (e.g. human being) is from late 14c.
Beirut: Lebanese capital, from Hebrew, literally "the wells," from be'erot, plural of be'er "well."
bejesus: mild expletive, 1908, perhaps from by Jesus. To beat the bejesus out of someone is from 1934.
bejewel (v.): 1550s, from be- + jewel. Related: Bejeweled.
beknow (v.): c.1300, "to become acquainted with; to be aware or conscious of," from be- + know. Related: Beknown; beknowing.
bel (n.): unit of power level in measuring sound, 1929, named for Scottish-born telephone pioneer Alexander Graham Bell (1847-1922).
Bel: heaven-and-earth god of Babylonian religion, from Akkadian Belu, literally "lord, owner, master," cognate with Hebrew ba'al.
bel (adj.): "beautiful," early 14c., from Old French bel, belle "beautiful, fair, fine" (see belle). "Naturalized in ME.; but after 1600 consciously French" [OED].
bel canto: 1894, Italian, literally "fine song."
bel paese: type of mild, creamy cheese, 1935, Italian proprietary name, literally "beautiful country or region."
belabor (v.): 1590s, "to exert one's strength upon," from be- + labor (v.). But figurative sense of "assail with words" is attested somewhat earlier (1590s); and belabored is attested from mid-15c. with a sense of "tilled, cultivated."
belabour (v.): chiefly British English spelling of belabor (q.v.); for spelling, see -or.
belated (adj.): 1610s, "overtaken by night," past participle adjective from belate "to make late, detain," from be- + late. Sense of "coming past due, behind date" is from 1660s. Related: Belatedly.
belay (v.): from Old English bilecgan, which, among other senses, meant "to lay a thing about" (with other objects), from be- + lecgan "to lay" (see lay (v.)). The only surviving sense is the nautical one of "coil a running rope round a cleat or pin to secure it" (also transferred to mountain-climbing), first attested 1540s; but this is possibly a cognate word, from Dutch beleggen.
belch (v.): Old English bealcan "bring up wind from the stomach," also "swell, heave," of echoic origin (cf. Dutch balken "to bray, shout"). Extended to volcanoes, cannons, etc. 1570s. Related: Belched; belching. As a noun, recorded from 1510s. It is recorded in 1706 as a slang noun meaning "poor beer."
beldam (n.): "aged woman," 1570s; earlier "grandmother" (mid-15c.), from dame (q.v.) in the sense of "mother" + bel-, Middle English prefix expressing relationship (cf. belfader, belsire "grandfather"), from Old French bel, belle "beautiful, fair, fine" (see belle). This "direct relationship" sense of bel is not found in French, where the prefix is used to form words for in-laws.
beleaguer (v.): 1580s, from Dutch or Low German belegeren "to besiege," from be- "around" (see be-) + legeren "to camp," from leger "bed, camp, army, lair," from Proto-Germanic *leg-raz-, from PIE *legh-to- "lie" (see lie (v.2)). A word from the Flemish Wars (cf. Swedish belägra, Dutch belegeren "besiege," German Belagerung "siege"). Spelling influenced by league. Related: Beleaguered; beleaguering.
beleave (v.): Old English belæfan, "to cause or allow to remain behind, to leave something behind," a general Germanic compound (cf. Gothic bilaibjan) from be- + Old English læfan "to leave" (see leave (v.)). In Middle English sometimes contracted to bleve. For further development, see belive.
belfry (n.): c.1400, "siege tower" (late 13c. in Anglo-Latin with a sense "bell tower"), from Old North French berfroi "movable siege tower" (Modern French beffroi), from Middle High German bercfrit "protecting shelter," literally "that which watches over peace," from bergen "to protect" (see bury) + frid "peace." Originally a wooden siege tower on wheels ("free" to move); it came to be used for chime towers (mid-15c.), which at first often were detached from church buildings (as the Campanile on Plaza San Marco in Venice). Spelling altered by dissimilation or by association with bell (n.).
Belgian (adj.): 1620s, in reference to the ancient Belgæ (see Belgium). Belgian Congo formed 1908 by annexation.
Belgic (adj.): 1580s, from Latin Belgicus, from Belgae (see Belgium).
Belgium: c.1600, "Low Germany and the Netherlands," from the Latin name of the territory near here occupied by the Belgæ, a Celtic tribe. Adopted 1830 as the name of a new nation formed from the southern part of the former United Kingdom of the Netherlands.
Belial: early 13c., from Hebrew bel'yya'al "destruction," literally "worthless," from b'li "without" + ya'al "use." Wickedness as an evil force (Deut. xiii:13); later treated as a proper name for Satan (2 Cor. vi:15), though Milton made him one of the fallen angels.
belie (v.): Old English beleogan "to deceive by lies," from be- + lie (v.1) "to lie, tell lies." Current sense of "to contradict as a lie" is first recorded 1640s. The other verb lie once also had a formation like this, from Old English belicgan, which meant "to encompass, beleaguer," and in Middle English was a euphemism for "to have sex with" (i.e. "to lie with carnally").
belief (n.): late 12c., bileave, replacing Old English geleafa "belief, faith," from West Germanic *ga-laubon "to hold dear, esteem, trust" (cf. Old Saxon gilobo, Middle Dutch gelove, Old High German giloubo, German Glaube), from *galaub- "dear, esteemed," from intensive prefix *ga- + *leubh- "to care, desire, like, love" (see love (v.)). The prefix was altered on analogy of the verb believe. The distinction of the final consonant from that of believe developed 15c.
"The be-, which is not a natural prefix of nouns, was prefixed on the analogy of the vb. (where it is naturally an intensive) .... [OED]
Belief used to mean "trust in God," while faith meant "loyalty to a person based on promise or duty" (a sense preserved in keep one's faith, in good (or bad) faith and in common usage of faithful, faithless, which contain no notion of divinity). But faith, as cognate of Latin fides, took on the religious sense beginning in 14c. translations, and belief had by 16c. become limited to "mental acceptance of something as true," from the religious use in the sense of "things held to be true as a matter of religious doctrine" (a sense attested from early 13c.).
believability (n.): 1865, from believable + -ity.
believable (adj.): late 14c., from believe + -able. Related: Believably.
believe (v.): Old English belyfan "to believe," earlier geleafa (Mercian), gelefa (Northumbrian), gelyfan (West Saxon) "believe," from Proto-Germanic *ga-laubjan "to believe," perhaps literally "hold dear, love" (cf. Old Saxon gilobian "believe," Dutch geloven, Old High German gilouben, German glauben), ultimately a compound based on PIE *leubh- "to care, desire, love" (see belief).

Spelling beleeve is common till 17c.; then altered, perhaps by influence of relieve, etc. To believe on instead of in was more common in 16c. but now is a peculiarity of theology; believe of also sometimes was used in 17c. Related: Believed (formerly occasionally beleft); believing. Expression believe it or not attested by 1874; Robert Ripley's newspaper cartoon of the same name is from 1918. Emphatic you better believe attested from 1854.
believer (n.): "one who has faith in religion," 1540s, agent noun from believe.
belittle (v.): 1781, "to make small," from be- + little (v.); first recorded in writings of Thomas Jefferson (and probably coined by him), who was roundly execrated for it in England:
Belittle! What an expression! It may be an elegant one in Virginia, and even perfectly intelligible; but for our part, all we can do is to guess at its meaning. For shame, Mr. Jefferson! ["European Magazine and London Review," 1787, reporting on "Notes on the State of Virginia"; to guess was considered another barbarous Yankeeism.]
Jefferson used it to characterize Buffon's view that American life was stunted by nature, which he was refuting. The figurative sense of "depreciate, scorn as worthless" (as the reviewers did to this word) is from 1797. Related: Belittled; belittling.
belive (v.): Old English belifan "remain," intransitive form of belæfan "cause to remain" (see beleave). A general Germanic word (cf. Gothic beleiban, Old High German biliban, German bleiben, Dutch blijven); confused in early Middle English with beleave and merged into it, which gave beleave two clashing senses ("to leave," also "to remain") which might be why the compound word, the cognate of important verbs in other Germanic languages, was abandoned in English and only leave (v.) remains.
bell (n.): Old English belle, common North Sea Germanic (cf. Middle Dutch belle, Middle Low German belle) but not found elsewhere in Germanic (except as a borrowing), from PIE root *bhel- (4) "to sound, roar." Statistical bell curve was coined 1870s in French. Of glasses in the shape of a bell from 1640s. Bell pepper is from 1707, so called for its shape. Bell, book, and candle is a reference to a form of excommunication. To ring a bell "awaken a memory" (1934) is perhaps a reference to Pavlovian experiments.