Online Etymology Dictionary

blackjack (n.): used in many senses since 16c., earliest is possibly "tar-coated leather jug for beer" (1590s), from black (adj.) + jack in any of its many slang senses. The weapon so called from 1889; the card game by 1900.
blackleg (n.): "swindler," especially in equestrian events, 1771, from black (adj.) + leg (n.), but the exact signification is uncertain.
blacklist (n.): also black-list, black list, "list of persons who have incurred suspicion," 1610s, from black (adj.), here indicative of disgrace, censure, punishment (attested from 1590s, in black book) + list (n.1). Specifically of employers' list of workers considered troublesome (usually for union activity) is from 1888. As a verb, from 1718. Related: Blacklisted; blacklisting.
blackly (adv.): 1560s, from black (adj.) + -ly (2).
blackmail (n.): 1550s, from black (adj.) + Middle English male "rent, tribute," from Old English mal "lawsuit, terms, bargaining, agreement," from Old Norse mal "speech, agreement;" related to Old English mæðel "meeting, council," mæl "speech," Gothic maþl "meeting place," from Proto-Germanic *mathla-, from PIE *mod- "to meet, assemble" (see meet (v.)). From the practice of freebooting clan chieftains who ran protection rackets against Scottish farmers. Black from the evil of the practice. Expanded c. 1826 to any type of extortion money. Compare silver mail "rent paid in money" (1590s); buttock-mail (Scottish, 1530s) "fine imposed for fornication."
blackmail (v.): 1852, from blackmail (n.). Related: Blackmailed; blackmailing.
blackness (n.): late 14c., from black (adj.) + -ness.
blackout (n.): also black-out, 1908 in the theatrical sense of a darkened stage, from black + out. Figurative sense of "loss of memory" is 1934 (verb and noun); as a dousing of lights as an air raid precaution, it is recorded from 1935. Verbal phrase black out, in reference to printed or written matter deemed objectionable and covered in black ink, is attested from 1888.
blacksmith (n.): late 15c. (mid-13c. as a surname), from black + smith (n.). Listed in royal ordinance (along with bladesmiths, spurriers, and goldbeaters); blacksmiths worked in heated, heavy metals as opposed to those who beat gold, tin, or pewter (the material of a whitesmith).
blacktop (n.): road resurfacing material, 1931, American English, from black (adj.) + top (n.1).
bladder (n.): Old English blædre (West Saxon), bledre (Anglian) "(urinary) bladder," also "blister, pimple," from Proto-Germanic *blaedron (source also of Old Norse blaðra, Old Saxon bladara, Old High German blattara, German Blatter, Dutch blaar), from PIE *bhle- "to blow" (see blast). Extended senses from early 13c. from animal bladders used for buoyancy, storage, etc.
blade (n.): Old English blæd "a leaf," but also "a leaf-like part" (of spade, oar, etc.), from Proto-Germanic *bladaz (source also of Old Frisian bled "leaf," German Blatt, Old Saxon, Danish, Dutch blad, Old Norse blað), from PIE *bhle-to-, suffixed form (past participle) of *bhel- (3) "to thrive, bloom," possibly identical with *bhel- (2) "to blow, swell" (see bole). Extended in Middle English to shoulders (c. 1300) and swords (early 14c.). The modern use in reference to grass may be a Middle English revival, by influence of Old French bled "corn, wheat" (11c., perhaps from Germanic). The cognate in German, Blatt, is the general word for "leaf;" Laub is used collectively as "foliage." Old Norse blað was used of herbs and plants, lauf in reference to trees. This might have been the original distinction in Old English, too. Of men from 1590s; in later use often a reference to 18c. gallants, but the original exact sense, and thus signification, is uncertain.
blah (n.): "idle, meaningless talk," 1918, probably echoic; the adjective meaning "bland, dull" is from 1919, perhaps influenced by French blasé "bored, indifferent." The blahs "depression" is attested by 1966.
blain (n.): Old English blegen "a sore," from Proto-Germanic *blajinon "a swelling" (source also of Danish blegn, Dutch blein), from PIE *bhlei- "to swell," from root *bhel- (2) "to blow, inflate, swell;" see bole.
blaise: Scottish variant of blaze.
blame (v.): c. 1200, "find fault with;" c. 1300, "lay blame on," from Old French blasmer (12c., Modern French blâmer) "to rebuke, reprimand, condemn, criticize," from Vulgar Latin *blastemare, from Late Latin blasphemare "revile, reproach" (see blaspheme). Replaced Old English witan with long "i." Related: Blamed; blaming.
blame (n.): early 13c., from Old French blasme "blame, reproach; condemnation," a back-formation from blasmer (see blame (v.)).
blamed (adv.): "confoundedly" 1833, later also as an adjective, from past participle of blame (v.), as a "euphemistic evasion of the horrible word damn." [Bartlett, "Dictionary of Americanisms," 1848].
This adjective 'blamed' is the virtuous oath by which simple people, who are improving their habits, cure themselves of a stronger epithet. [Edward Everett Hale, "If, Yes, and Perhaps," 1868]
Compare also blamenation (1837) as an expletive. The imprecation blame me is attested from 1830.
blameless (adj.): late 14c., from blame (n.) + -less. Related: Blamelessly; blamelessness. Seldom-used blameful is recorded from late 14c.
blameworthy (adj.): also blame-worthy, late 14c., from blame (n.) + worthy (adj.). Related: Blameworthiness.
blanch (v.1): c. 1400, transitive, "to make white, turn pale," from Old French blanchir "to whiten, wash," from blanc "white" (11c.; see blank (adj.)). Originally "to remove the hull of (almonds, etc.) by soaking." Intransitive sense of "to turn white" is from 1768. Related: Blanched; blanching.
blanch (v.2): "to start back, turn aside," 1570s, variant of blench. Related: Blanched; blanching.
Blanche: fem. proper name, from French Blanche, from Old French blanc "white," of Germanic origin (see blank (adj.)). A fairly popular name for girls born in the U.S. from about 1880 to 1900.
blancmange (n.): late 14c., from Old French blancmengier (13c.), literally "white eating," originally a dish of fowl minced with cream, rice, almonds, sugar, eggs, etc.; from blanc "white" (also used in Old French of white foods, such as eggs, cream, also white meats such as veal and chicken; see blank (adj.)) + mangier "to eat" (see manger).
bland (adj.): 1660s, from Italian blando "delicate," or Old French bland "flattering, complimentary," both from Latin blandus "smooth-talking, flattering, alluring," perhaps from PIE *mlad-, nasalized variant of *meld-, extended form of root *mel- (see melt). Related: Blandly; blandness. Latin also had blandiloquentulus "flattering in speech," which might have yielded a useful English *blandiloquent.
blandish (v.): c. 1300, from Old French blandiss-, present participle stem of blandir "to flatter, caress," from Latin blandiri "flatter, soothe, caress, coax," from blandus (see bland). OED reports it rare in 17c., 18c. Related: Blandished; blandishing.
blandishment (n.): "flattering speech," 1590s, from blandish + -ment. Sense of "attraction, allurement" (often blandishments) is from 1590s.
blank (adj.): early 13c., "white, pale, colorless," from Old French blanc "white, shining," from Frankish *blank "white, gleaming," or some other West Germanic source (compare Old Norse blakkr, Old English blanca "white horse;" Old High German blanc, blanch; German blank "shining, bright"), from Proto-Germanic *blangkaz "to shine, dazzle," extended form of PIE root *bhel- (1) "to shine, flash, burn" (see bleach (v.)).

Meaning "having empty spaces" evolved c. 1400. Sense of "void of expression" (a blank look) is from 1550s. Spanish blanco, Italian bianco are said to be from Germanic. Related: Blankly, blankness.
blank (n.): late 14c. as the name of a small French coin; 1550s as "white space in the center of a target," from the same source as blank (adj.). Meaning "empty space" (in a document, etc.) is from c. 1570. Meaning "losing lottery ticket" (1560s) is behind the expression draw a blank. The word has been "for decorum's sake, substituted for a word of execration" [OED] from 1854. From 1896 as short for blank cartridge (itself from 1826).
blank (v.): 1540s, "to nonplus, disconcert, shut up;" 1560s, "to frustrate," from blank (adj.). Sports sense of "defeat (another team) without allowing a score" is from 1870. Meaning "to become blank or empty" is from 1955. Related: Blanked; blanking.
blank verse (n.): 1580s; the thing itself is attested in English poetry from mid-16c. and is classical in origin.
blanket (n.): c. 1300, "bed-clothing; white woolen stuff," from Old French blanchet "light wool or flannel cloth; an article made of this material," diminutive of blanc "white" (see blank (adj.), which had a secondary sense of "a white cloth." Wet blanket (1830) is from the notion of a person who throws a damper on social situations like a wet blanket smothers a fire. In U.S. history, a blanket Indian (1859) was one using the traditional garment instead of wearing Western dress.
Only 26,000 blanket Indians are left in the United States. ["Atlantic Monthly," March 1906]
blanket (v.): c. 1600, "to cover with or as with a blanket;" also "to toss in a blanket" (as punishment), from blanket (n.). Related: Blanketed; blanketing.
blare (v.): late 14c., bleren "to wail," possibly from an unrecorded Old English *blæren, or from Middle Dutch bleren "to bleat, cry, bawl, shout." Probably echoic, either way. Related: Blared; blaring. As a noun from 1809, from the verb.
blaring (adj.): mid-15c., from present participle of blare. Of things other than sounds, from 1866.
blarney (n.): 1796, from Blarney Stone (which is said to make a persuasive flatterer of any who kiss it), in a castle near Cork, Ireland. As Bartlett explains it, the reason is the difficulty of the feat of kissing the stone where it sits high up in the battlement: "to have ascended it, was proof of perseverence, courage, and agility, whereof many are supposed to claim the honor who never achieved the adventure." So to have kissed the Blarney Stone came to mean "to tell wonderful tales" ["Dictionary of Americanisms," 1848]. The word reached wide currency through Lady Blarney, the smooth-talking flatterer in Goldsmith's "Vicar of Wakefield" (1766). As a verb from 1803.
blase (adj.): "bored from overindulgence," 1819, from French blasé, past participle of blaser "to satiate" (17c.), which is of unknown origin. Perhaps from Dutch blazen "to blow" (related to English blast), with a sense of "puffed up under the effects of drinking."
blase: see blasé.
blaspheme (v.): mid-14c., from Old French blasfemer "to blaspheme" (14c., Modern French blasphémer), from Church Latin blasphemare (also in Late Latin "revile, reproach"), from Greek blasphemein "to speak lightly or amiss of sacred things, to slander," from blasphemos "evil-speaking" (see blasphemy). A reintroduction after the original word had been worn down and sense-shifted to blame (v.). Related: Blasphemed; blaspheming.
blasphemous (adj.): early 15c., blasfemous, from Old French blasfemeus or directly from Late Latin blasphemus, from blasphemare (see blaspheme).
blasphemy (n.): early 13c., from Old French blasfemie "blasphemy," from Late Latin blasphemia, from Greek blasphemia "a speaking ill, impious speech, slander," from blasphemein "to speak evil of." Second element is pheme "utterance," from PIE root *bha- (2) "to speak, tell, say" (see fame); first element uncertain, perhaps related to blaptikos "hurtful," though blax "slack (in body and mind), stupid" also has been suggested.
blast (n.): Old English blæst "blowing, breeze, puff of wind," from Proto-Germanic *bles- (source also of Old Norse blastr, Old High German blast "a blowing, blast," German blasen, Gothic blesan "to blow"), from PIE *bhle- "to blow," probably a variant of root *bhel- (2) "to blow, inflate, swell" (see bole).

Meaning "explosion" is from 1630s; that of "noisy party, good time" is from 1953, American English slang. Sense of "strong current of air for iron-smelting" (1690s) led to blast furnace and transferred sense in full blast "the extreme" (1839). Blast was the usual word for "a smoke of tobacco" c. 1600.
blast (v.): Old English blæstan "to blow, belch forth," from the root of blast (n.). Since 16c., often "to breathe on balefully." Meaning "to blow up by explosion" is from 1758. Related: Blasted; blasting. Blast off (n.) is attested from 1950.
blasted (adj.): "stricken by malignant forces (natural or supernatural), cursed, blighted," 1550s, from blast (v.), with the notion of "balefully breathed upon." In the sense of "cursed, damned" it is attested from 1680s. Meaning "drunk or stoned" dates from 1972 (blast (v.) "smoke marijuana" attested from 1959).
blastema (n.): 1849, Modern Latin, from Greek blastema "offspring, offshoot," from stem of blastanein "to shoot forth," from blastos "sprout, germ," which is of unknown origin. Related: Blastemal.
blasto-: before vowels blast-, word-forming element used in scientific compounds to mean "germ, bud," from Greek blasto-, comb. form of blastos "sprout, germ," which is of unknown origin.
blastocyst (n.): 1876, from blasto- + cyst.
blastula (n.): embryonic state, 1875, Modern Latin, from Greek blastos "sprout, germ" + diminutive ending -ula (see -ule).
blat (v.): 1846, U.S. colloquial, imitative. Related: Blatted; blatting. As a noun from 1904.
blatant (adj.): 1596, in blatant beast, coined by Edmund Spenser in "The Faerie Queen" to describe a thousand-tongued monster representing slander; probably suggested by Latin blatire "to babble." It entered general use 1650s, as "noisy in an offensive and vulgar way;" the sense of "obvious, glaringly conspicuous" is from 1889. Related: Blatantly.