Online Etymology Dictionary

blockhead (n.): also block-head, "stupid person," 1540s (implied in blockheaded), from block (n.) + head (n.); probably originally an image of the head-shaped oaken block used by hat-makers, though the insulting sense is the older one.
blockhouse (n.): c. 1500, of uncertain origin (see blockade (n.)). Also in 16c. French, Dutch, German.
blocking (n.): 1630s, verbal noun from present participle of block (v.). By 1891 in U.S. football; by 1961 in theater.
blocks (n.): children's wooden building toys, 1821, from block (n.).
blocky (adj.): 1879, from block (n.) + -y (2). Related: Blockily; blockiness.
blog (n.): 1998, short for weblog (which is attested from 1994, though not in the sense "online journal"), from (World Wide) Web + log. Joe Bloggs (c. 1969) was British slang for "any hypothetical person" (compare U.S. equivalent Joe Blow); earlier blog meant "a servant boy" in one of the college houses (c. 1860, see Partridge, who describes this use as a "perversion of bloke"), and, as a verb, "to defeat" in schoolboy slang. The Blogger online publishing service was launched in 1999.
bloke (n.): "fellow," 1851, London slang, of unknown origin, perhaps from Celtic ploc "large, stubborn person;" another suggestion is Romany (Gypsy) and Hindi loke "a man."
blond (adj.): late 15c., from Old French blont "fair, blond" (12c.), from Medieval Latin blundus "yellow," perhaps from Frankish *blund. If it is a Germanic word, it is possibly related to Old English blonden-feax "gray-haired," from blondan, blandan "to mix" (see blend (v.)). According to Littré, the original sense of the French word was "a colour midway between golden and light chestnut," which might account for the notion of "mixed."

Old English beblonden meant "dyed," so it is also possible that the root meaning of blonde, if it is Germanic, may be "dyed," as ancient Teutonic warriors were noted for dying their hair. Du Cange, however, writes that blundus was a vulgar pronunciation of Latin flavus "yellow." Another guess (discounted by German etymologists), is that it represents a Vulgar Latin *albundus, from alba "white."

The word was reintroduced into English 17c. from French, and was until recently still felt as French, hence blonde (with French feminine ending) for females. Italian biondo, Spanish blondo, Old Provençal blon all are of Germanic origin.
Fair hair was much esteemed by both the Greeks and Romans, and so they not only dyed and gold-dusted theirs ..., but also went so far as to gild the hair of their statues, as notably those of Venus de Medici and Apollo. In the time of Ovid (A.U.C. 711) much fair hair was imported from Germany, by the Romans, as it was considered quite the fashionable color. Those Roman ladies who did not choose to wear wigs of this hue, were accustomed to powder theirs freely with gold dust, so as to give it the fashionable yellow tint. [C. Henry Leonard, "The Hair," 1879]
blond (n.): c. 1755 of a type of lace, 1822 of persons; from blond (adj.).
blonde: late 15c.; see blond (adj.).
blondish (adj.): 1857, from blond (adj.) + -ish.
blondness (n.): 1842, from blond (adj.) + -ness.
blood (n.): Old English blod "blood," from Proto-Germanic *blodam "blood" (source also of Old Frisian blod, Old Saxon blôd, Old Norse bloð, Middle Dutch bloet, Dutch bloed, Old High German bluot, German Blut, Gothic bloþ), from PIE *bhlo-to-, perhaps meaning "to swell, gush, spurt," or "that which bursts out" (compare Gothic bloþ "blood," bloma "flower"), in which case it would be from suffixed form of *bhle-, extended form of root *bhel- (3) "to thrive, bloom" (see folio).

There seems to have been an avoidance in Germanic, perhaps from taboo, of other PIE words for "blood," such as *esen- (source of poetic Greek ear, Old Latin aser, Sanskrit asrk, Hittite eshar); also *krew-, which seems to have had a sense of "blood outside the body, gore from a wound" (source of Latin cruour "blood from a wound," Greek kreas "meat"), which came to mean simply "blood" in the Balto-Slavic group and some other languages.

Inheritance and relationship senses (also found in Latin sanguis, Greek haima) emerged in English by mid-13c. Meaning "person of one's family, race, kindred" is late 14c. As the seat of passions, it is recorded from c. 1300. Slang meaning "hot spark, a man of fire" [Johnson] is from 1560s. Blood pressure attested from 1862. Blood money is from 1530s; originally money paid for causing the death of another.

Blood type is from 1928. That there were different types of human blood was discovered c. 1900 during early experiments in transfusion. To get blood from a stone "do the impossible" is from 1660s. Expression blood is thicker than water attested by 1803, in reference to family ties of those separated by distance. New (or fresh) blood, in reference to members of an organization or group is from 1880.
blood (v.): 1590s, "to smeart with blood;" 1620s, "to cause to bleed," from blood (n.). Meaning "to give an animal its first taste of blood" is from 1781. Related: Blooded; blooding.
blood-curdling (adj.): also bloodcurdling, 1817, from blood (n.) + present participle of curdle. Also formerly with a noun form, bloodcurdler "incident which freezes the blood," especially "sensational story," 1877, slang; also in use in this sense was blood-freezer (1886).
blood-letting (n.): also bloodletting, early 13c., blod letunge, from blood (n.) + letting. Hyphenated from 17c., one word from mid-19c. Old English had blodlæte "blood-letting."
blood-red (adj.): Old English blodread; see blood (n.) + red (adj.1).
blood-stained (adj.): 1590s, from blood (n.) + past participle of stain (v.).
bloodhound (n.): also blood-hound, type of large dog used in hunting, c. 1300, from blood (n.) + hound (n.).
bloodily (adv.): 1560s, from bloody + -ly (2).
bloodiness (n.): 1590s, from bloody (adj.) + -ness.
bloodless (adj.): Old English blodleas; see blood (n.) + -less. The figurative sense in Middle English was "powerless." Related: Bloodlessly.
bloodlust (n.): 1847 (Bulwer Lytton), also blood-lust, from blood (n.) + lust (n.).
bloodshed (n.): also blood-shed, c. 1500, "the shedding of (one's) blood," from verbal phrase (attested in late Old English), from blood (n.) + shed (v.). The sense of "slaughter" is much older (early 13c., implied in bloodshedding).
bloodshot (adj.): also blood-shot, 1550s, short for bloodshotten (c. 1500), from blood (n.) + old past participle of shoot.
bloodstream (n.): also blood-stream, 1847, from blood (n.) + stream (n.).
bloodsucker (n.): also blood-sucker, late 14c., of animals, from blood (n.) + sucker (n.); in the figurative sense, of persons, it is attested from 1660s.
bloodthirsty (adj.): also blood-thirsty, 1530s (Coverdale, Ps. xxv:9), from blood (n.) + thirsty (adj.). Ancient Greek had a similar image in haimodipsos. Related: Bloodthirstiness.
bloody (adj.): Old Engish blodig, adjective from blod (see blood). Common Germanic, compare Old Frisian blodich, Old Saxon blôdag, Dutch bloedig, Old High German bluotag, German blutig.

It has been a British intensive swear word since at least 1676. Weekley relates it to the purely intensive use of the cognate Dutch bloed, German Blut. But perhaps it ultimately is connected with bloods in the slang sense of "rowdy young aristocrats" (see blood (n.)) via expressions such as bloody drunk "as drunk as a blood."

Partridge reports that it was "respectable" before c. 1750, and it was used by Fielding and Swift, but heavily tabooed c. 1750-c. 1920, perhaps from imagined association with menstruation; Johnson calls it "very vulgar," and OED writes of it, "now constantly in the mouths of the lowest classes, but by respectable people considered 'a horrid word', on par with obscene or profane language."
The onset of the taboo against bloody coincides with the increase in linguistic prudery that presaged the Victorian Era but it is hard to say what the precise cause was in the case of this specific word. Attempts have been made to explain the term's extraordinary shock power by invoking etymology. Theories that derive it from such oaths as "By our Lady" or "God's blood" seem farfetched, however. More likely, the taboo stemmed from the fear that many people have of blood and, in the minds of some, from an association with menstrual bleeding. Whatever, the term was debarred from polite society during the whole of the nineteenth century. [Rawson]
Shaw shocked theatergoers when he put it in the mouth of Eliza Doolittle in "Pygmalion" (1914), and for a time the word was known euphemistically as "the Shavian adjective." It was avoided in print as late as 1936. Bloody Sunday, Jan. 30, 1972, when 13 civilians were killed by British troops at protest in Londonderry, Northern Ireland.
bloody (v.): 1520s, from bloody (adj.). Related: Bloodied; bloodying. Old English had blodigan "to make bloody," but the modern word seems to be a later formation.
Bloody Mary: the cocktail, attested from 1953 (originally touted in part as a hangover cure), said to be named for Mary Tudor, queen of England 1553-58, who earned her epithet for vigorous prosecution of Protestants. The drink earned its, apparently, simply for being red from tomato juice. The cocktail's popularity also concided with that of the musical "South Pacific," which has a character named "Bloody Mary."
blooey (n.): "ruin, smash," 1915, U.S. slang, probably imitative.
bloom (n.1): "blossom of a plant," c. 1200, a northern word, from a Scandinavian source akin to Old Norse blomi "flower, blossom," also collectively "flowers and foliage on trees;" from Proto-Germanic *blomon (source also of Old Saxon blomo, Middle Dutch bloeme, Dutch bloem, Old High German bluomo, German Blume, Gothic bloma), from PIE *bhle- (source also of Old Irish blath "blossom, flower," Latin flos "flower," florere "to blossom, flourish"), extended form of root *bhel- (3) "to thrive, bloom" (see folio). Related to Old English blowan "to flower" (see blow (v.2)).

Transferred sense, of persons, is from c. 1300; meaning "state of greatest loveliness" is from early 14c.; that of "blush on the cheeks" is from 1752. Old English had cognate bloma, but only in the figurative sense of "state of greatest beauty;" the main word in Old English for "flower" was blostm (see blossom).
bloom (n.2): "rough mass of wrought iron," from Old English bloma "lump of metal; mass," which is of unknown origin. Identical in form to bloom (n.1), and sometimes regarded as a secondary sense of it, but evidence of a connection is wanting.
bloom (v.): mid-13c., blomen, from the noun (see bloom (n.1)). Related: Bloomed; blooming.
bloomer (n.): 1730, agent noun from bloom (v.).
bloomers (n.): 1851, named for U.S. feminist reformer Amelia Jenks Bloomer (1818-1894), who promoted them. The surname is attested from c. 1200, said to mean literally "iron-worker," from Old English bloma (see bloom (n.2)).
blooming (adj.): late 14c., present participle adjective from bloom (v.). Meaning "full-blown" (often a euphemism for bloody) is attested from 1882.
Bloomsbury: 1910, in reference to the set of Bohemian writers, artists, and intellectuals (including E.M. Forster, Virginia Woolf, Vanessa and Clive Bell, John Maynard Keynes) centered on Lytton Strachey; so called from the London neighborhood where several lived and worked.
Women in love with buggers and buggers in love with womanizers, I don't know what the world is coming to. [Lytton Strachey]
The place name is recorded 1291 as Blemondesberi "manor held by the Blemond family," from Blémont in France. It was laid out for housing in 17c., fashionable from 18c.
bloop (n.): 1931, from bloop (v.), 1926, a word from the early days of radio (see blooper). Related: Blooped; blooping.
blooper (n.): "blunder," 1943, apparently first in theater, from American English baseball slang meaning "a fly ball in a high arc missed by the fielder" (1937) or else from the earlier sense "radio receiver that interferes with nearby sets" when a careless operator throws it into oscillation (1926), in which case it imitates the resulting sound.
blossom (n.): c. 1200, from Old English blostm, blostma "blossom, flower, fruit," from Proto-Germanic *blo-s- (source also of Middle Low German blosom, Dutch bloesem, German Blust), from PIE *bhlow-, extended form of *bhel- (3) "to thrive, bloom" (see folio). This is the native word, now largely superseded by bloom (n.1) and flower (n.).
blossom (v.): late 14c., from Old English blostmian, from blostma "blossom, flower" (see blossom (n.)). Figurative use from late 14c. Related: Blossomed; blossoming.
blot (n.): late 14c., originally "blemish," perhaps from Old Norse blettr "blot, stain," or from Old French blot, variant of bloc "block," or blestre "blister, lump, clump of earth."
blot (v.): early 15c., "to make blots;" mid-15c. "to blot out, obliterate" (words), from blot (n.). Related: Blotted; blotting.
blotch (n.): c. 1600, perhaps a blend of blot and botch or patch.
blotchy (adj.): 1799, from blotch + -y (2). Related: Blotchiness.
blotter (n.): 1590s, "thing for drying wet spots," agent noun from blot (v.). Meaning "bad writer" is from c. 1600. Sense of "day book" is from 1670s, and the word was applied early 19c. to rough drafts, scrap books, notebooks, and draft account books. Hence the police jargon sense "arrest record sheet," recorded from 1887.
blotting (n.): mid-15c., verbal noun from blot (v.). Blotting paper is recorded from 1510s.
blotto (adj.): "drunk," c. 1905, from some signification of blot (v.) in its "soak up liquid" meaning.