Online Etymology Dictionary

knockout (n.): also knock-out, in fighting, 1887, from verbal phrase knock out "to stun by a blow for a 10-count" in boxing, short for to knock out of time; see knock (v.) + out (adv.). Slang meaning "excellent thing or person" is from 1892; specifically "beautiful woman" by 1953. As an adjective from 1896 in the tournament competition sense, 1898 in fighting. To knock oneself out "make a great effort" is from 1936.
knoll (n.): Old English cnoll "hilltop, small hill, clod, ball," related to Old Norse knollr "hilltop;" German knolle "clod, lump;" Dutch knol "turnip," nol "a hill."
knot (n.): Old English cnotta "intertwining of ropes, cords, etc.," from Proto-Germanic *knuttan- (source also of Low German knütte, Old Frisian knotta "knot," Dutch knot, Old High German knoto, German Knoten, perhaps also Old Norse knutr "knot, knob"). For pronunciation, see kn-.

Figurative sense of "difficult problem, a perplexity" was in Old English (compare Gordian knot). Symbolic of the bond of wedlock from early 13c. As an ornament of dress, first attested c. 1400. Meaning "thickened part or protuberance on tissue of a plant" is from late 14c. As "small group or cluster of persons" late 14c.

The nautical unit of measure of speed (1630s) is from the practice of attaching knotted string to the log line at equal distances. The ship's speed can be measured by the number of knots that play out while the sand glass is running.
The distance between the knots on the log-line should contain 1/120 of a mile, supposing the glass to run exactly half a minute. [Jorge Juan and Antonio de Ulloa, "A Voyage to South America" 1760]
Hence the word knot came also to be used as the equivalent of a nautical mile (in pre-World War II use in U.S. and Britain, about 6,080 feet). A speed of 10 knots will cover ten nautical miles in an hour (equivalent to a land speed of about 11.5 mph).
knot (v.): "to tie in a knot," mid-15c., from knot (n.). Intransitive sense "form into knots" is from 1610s. Related: Knotted (late 12c.), knotting.
knot-hole (n.): also knothole, "hole left in a plank or board after a knot has dropped out," 1726, see knot (n.) + hole (n.).
knothead (n.): "stupid person," by 1899, American English, from knot (n.) + head (n.). Joe Knothead is the name of a character in an 1857 blackface satire publication. And a local history from Massachusetts published in 1879 describes an old-time character known as knot-head because "[d]uring the hottest days of summer ... he worked bare-headed in the sun ...."

Knothead also was used as a term in cattle and sheep raising, defined in 1922 as "a type of poorly bred, stunted northern cattle, about the size of yearlings, but with heavy horns indicating that they are older." It turns up, however, in an 1849 petition to the Ohio Legislature, recommending a certain person for a court position, in part because he is a knot-head, which the report of the petition notes is a term of praise for a judge because they are asked to untangle knotty legal questions, but which phrase, it adds, "is believed not to be in use among gentlemen in the north part of the State." [Appendix to the Journal of the Ohio House of Representatives, Session of 1848-9]
knotty (adj.): mid-13c., "full of knots" (figurative use, of questions or problems, is attested from early 13c.), from knot (n.) + -y (2). Related: Knottiness.
knotweed (n.): 1570s, from knot (n.) + weed (n.).
knotwork (n.): 1846, from knot (n.) + work (n.).
know (v.): Old English cnawan (class VII strong verb; past tense cneow, past participle cnawen), "perceive a thing to be identical with another," also "be able to distinguish" generally (tocnawan); "perceive or understand as a fact or truth" (opposed to believe); "know how (to do something)," from Proto-Germanic *knew- (source also of Old High German bi-chnaan, ir-chnaan "to know").

This is from PIE root *gno- "to know" (source also of Old Persian xšnasatiy "he shall know;" Old Church Slavonic znati, Russian znat "to know;" Latin gnoscere; Greek *gno-, as in gignoskein; Sanskrit jna- "know").

For pronunciation, see kn-. Once widespread in Germanic, the verb is now retained there only in English, where it has widespread application, covering meanings that require two or more verbs in other languages (such as German wissen, kennen, erkennen and in part können; French connaître "perceive, understand, recognize," savoir "have a knowledge of, know how;" Latin scire "to understand, perceive," cognoscere "get to know, recognize;" Old Church Slavonic znaja, vemi). The Anglo-Saxons also used two distinct words for this, the other being witan (see wit (v.)).

From c. 1200 as "to experience, live through." Meaning "to have sexual intercourse with," also found in other modern languages, is attested from c. 1200, from the Old Testament (Gen. iv.1). Attested from 1540s in colloquial phrases suggesting cunning or savvy (but often in the negative); to not know one's ass from one's elbow is from 1930.

As far as (one) knows "to the best of (one's) knowledge" is late 14c. Expression God knows is from c. 1400. To know too much (to be allowed to live, escape, etc.) is from 1872. To know better "to have learned from experience" is from 1704.

You know as a parenthetical filler is from 1712, but it has roots in 14c. You know as a euphemism for a thing or situation unmentionable is from 1867; you-know-who for a person it is thought best not to name (but implying the hearer knows) is from 1840.

As an expression of surprise, what do you know attested by 1914. Don't I know it in the opposite sense ("you need not tell me") is from 1874. You never know as a response to something unexpected is attested from 1924.
know (n.): "inside information," 1883, in in the know, from know (v.) Earlier it meant "knowledge, fact of knowing" (1590s).
know-how (n.): also knowhow, "technical expertise," 1838, American English, from know (v.) + how (adv.).
know-it-all (n.): "one deemed (over)full of information or correct answers," 1895, from verbal phrase; see know (v.). Earlier in the same sense was know-all (1862); and Mr. Know-All was a minor character in Bunyan's "The Holy War" (1682).
know-nothing (n.): 1827, "ignoramus," from know (v.) + nothing. As a U.S. nativist political party, active 1853-56, the name refers to the secret society at the core of the party, about which members were instructed to answer, if asked about it, that they "know nothing." The party eventually merged into the Republican Party. Related: Know-nothingism.
knowable (adj.): c. 1400, from know (v.) + -able.
knowing (adj.): "with knowledge of truth," late 14c., present participle adjective from know (v.). From c. 1500 as "shrewd, sharp, smart." Related: Knowingly.
knowledge (n.): early 12c., cnawlece "acknowledgment of a superior, honor, worship;" for first element see know (v.). The second element is obscure, perhaps from Scandinavian and cognate with the -lock "action, process," found in wedlock.

From late 14c. as "capacity for knowing, understanding; familiarity;" also "fact or condition of knowing, awareness of a fact;" also "news, notice, information; learning; organized body of facts or teachings." Sense of "sexual intercourse" is from c. 1400. Middle English also had a verb form, knoulechen "acknowledge" (c. 1200), later "find out about; recognize," and "to have sexual intercourse with" (c. 1300); compare acknowledge.
knowledgeable (adj.): also knowledgable, c. 1600, "capable of being known, recognizable" (a 17c. sense now obsolete), from knowledge in its Middle English verbal sense + -able. The sense of "having knowledge, displaying mental capacity" is from 1829 and probably a new formation.
known (adj.): mid-13c., knouen, "well-known, famous, notorious," past participle adjective from know (v.). From early 14c. as "recognized, not secret; familiar, not strange." As a noun, "that which is known," by 1863; earlier "famous person" (1835). In Middle English it meant "one's acquaintances." To make (something) known is from mid-14c.
knub (n.): "small lump, butt-end or piece," 1560s, probably cognate with Low German knubbe "knot, knob," Danish knub "block, log, stump" (see knob).
knuckle (n.): mid-14c., knokel "finger joint; any joint of the body, especially a knobby one; morbid lump or swelling." Perhaps in Old English, but not attested there. Common Germanic (compare Middle Low German knökel, Middle Dutch cnockel, German knöchel), literally "little bone," a diminutive of Proto-Germanic root *knuk- "bone," which is not represented in English in its simple form (but compare German Knochen "bone). For pronunciation, see kn-.
knuckle (v.): 1740, from knuckle (n.), originally in the game of marbles (putting a knuckle on the ground is the hand position preliminary to shooting). To knuckle down "apply oneself earnestly" is 1864 in American English, an extended sense from marbles; to knuckle under "submit, give in" is first recorded 1740, supposedly from the former more general sense of "knuckle" and here meaning "knee," hence "to kneel."
knuckle-duster (n.): face-busting, hand-protecting metal knuckle-guard, 1857, from knuckle (n.) + duster, name of a type of protective coat worn by workmen.
knuckleball (n.): also knuckle-ball, baseball pitch, by 1909, from knuckle (n.) + ball (n.1). So called from the position of the fingers in throwing it. Short form knuckler attested from 1914 (earlier this was the name of a type of toy marble, 1895, and slang for "a pick-pocket," 1834). Related: Knuckleballer.
knucklehead (n.): also knuckle-head, "stupid person," 1890, American English, from knuckle (n.) + head (n.).
"That infernal knuckle-head at the camp ought to have reported before now," he thought to himself, as he smoked. [Charles H. Shinn, "The Quicksands of Toro," in "Belford's Magazine," vol. V, June-November 1890, New York]
From 1869 as the name of a part in a type of mechanical coupling device. Popularized in the "stupid person" sense from 1942, from character R.F. Knucklehead, star of "Don't" posters hung up at U.S. Army Air Force training fields.
Everything Knucklehead does is wrong and ends in disaster. He endures one spectacular crash after another so that the students at the Gulf Coast Air Force Training Center may profit by his mistakes, and it looks now as if there will be no let-up in his agony. ["Life," May 25, 1942]
knurl (n.): "hard excrescence," c. 1600, probably a diminutive of Middle English knor "knot" (c. 1400), related to gnarled, from Proto-Germanic *knur- (source also of German knorren "a knotty excrescence," Dutch knor "knob," Swedish dialectal knurr "hard swelling"). Related: Knurly.
koala (n.): Australian marsupial, 1808, from the Aboriginal name of the animal, variously given as koola, kulla, kula.
koan (n.): Zen paradox meant to stimulate the mind, 1918, from Japanese ko "public" + an "matter for thought."
Kobe: type of fine beef, 1894, named for the region in Japan where it is raised, from Japanese ko "god" + he "house."
kobold (n.): German earth-elemental or nature spirit, 1830; see cobalt.
Kodak: brand of hand-held camera, arbitrary coinage by U.S. inventor George Eastman (1854-1932), U.S. trademark registered Sept. 4, 1888. In 1890s, practically synonymous with camera and also used as a verb (1891). Kodachrome, registered trademark for a method of color photography, 1915; the product was discontinued in 2006.
Kodiak: Alaskan island, from Russian Kadiak, from Alutiiq (Eskimo) qikertaq "island."
Koh-i-noor (n.): famous diamond, one of the British crown jewels after the annexation of Punjab in 1849, from Persian koh-i-nur, literally "mountain of light," from Persian koh "mountain" + Arabic nur "light."
kohl (n.): "powder used to darken the eyelids, etc.," properly of finely ground antimony, 1799, from Arabic kuhl (see alcohol).
kohlrabi (n.): also kohl-rabi, kohl rabi, kind of cabbage, turnip cabbage, 1807, from German Kohlrabi (16c.), which is based on Italian cavoli rape, plural of cavolo rapo "cole-rape;" see cole + rape (n.2). Form influenced in German by German kohl "cabbage."
koi (n.): 1727, from a Japanese local name for "carp."
koine (n.): common literary dialect of Greek in the Roman and early medieval period, 1903, from feminine singular of Greek koinos "common, ordinary" (see coeno-). Used earlier as a Greek word in English. From 1926 of other dialects in similar general use.
koinonia (n.): "Christian fellowship," 1865, Greek, literally "communion, fellowship," from koinos "common, ordinary" (see coeno-).
kola (n.): "the cola nut," 1830, variant of cola (q.v.).
kolkhoz (n.): U.S.S.R. collective farm, 1921, from Russian kolkhoz, contraction of kollektivnoe khozyaistvo "collective farm."
Komodo dragon (n.): 1927, named for Indonesian island of Komodo, where it lives.
Komsomol (n.): Russian communist youth organization, 1925, from Russian Komsomol, contraction of Kommunisticheskii Soyuz Molodezhi "Communist Union of Youth."
kook (n.): 1960, American English slang; see kooky.
kookaburra (n.): 1883, from a native Australian word.
kooky (adj.): 1959, American English, originally teenager or beatnik slang, possibly a shortening of cuckoo.
Using the newest show-business jargon, Tammy [Grimes] admits, "I look kooky," meaning cuckoo. ["Life" magazine, Jan. 5, 1959]
Related: Kookily; kookiness.
kop (n.): "hill," 1835, from Afrikaans, from Dutch kop "head," from the Germanic form of the root of English cup (n.); compare German Kopf "head."
kopeck (n.): coin worth one-hundredth part of a ruble, from Russian kopeika, from kop'e "lance" (cognate with Greek kopis "chopper, cleaver;" see hatchet (n.)); so called because the coin showed the czar with lance in hand.
kopje (n.): small hill in South Africa, 1852, earlier koppie (1848), from South African Dutch, diminutive of kop "hill; head" (see kop).
Koran: book which contains the Islamic religious and moral code; the standard work of classical Arabic, 1610s, from Arabic qur'an "a reading, recitation, book," from root of quara-a "he read, recited." Related: Koranic.
Kore: in Greek mythology, the daughter of Zeus and Demeter, also called Persephone in her aspect as Hades's wife, from Greek kore "maiden" (see crescent).