knothole (n.) Look up knothole at Dictionary.com
1726, see knot (n.) + hole (n.).
knotty (adj.) Look up knotty at Dictionary.com
mid-13c. (figurative use early 13c.), from knot (n.) + -y (2). Related: Knottiness.
know (v.) Look up know at Dictionary.com
Old English cnawan (class VII strong verb; past tense cneow, past participle cnawen), "to know, perceive; acknowledge, declare," from Proto-Germanic *knew- (cognates: Old High German bi-chnaan, ir-chnaan "to know"), from PIE root *gno- "to know" (cognates: Old Persian xšnasatiy "he shall know;" Old Church Slavonic znati, Russian znat "to know;" Latin gnoscere; Greek *gno-, as in gignoskein; Sanskrit jna- "know"). Once widespread in Germanic, this form is now retained only in English, where however 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, savoir; Latin novisse, cognoscere; Old Church Slavonic znaja, vemi). The Anglo-Saxons used two distinct words for this, witan (see wit) and cnawan.

Meaning "to have sexual intercourse with" is attested from c.1200, from the Old Testament. To not know one's ass from one's elbow is from 1930. 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. To know too much (to be allowed to live, escape, etc.) is from 1872. As an expression of surprise, what do you know attested by 1914.
know (n.) Look up know at Dictionary.com
"inside information" (as in in the know), 1883; earlier "fact of knowing" (1590s), from know (v.).
know-nothing (n.) Look up know-nothing at Dictionary.com
"ignoramus," 1827, from know + 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.
knowable (adj.) Look up knowable at Dictionary.com
c.1400, from know (v.) + -able.
knowhow (n.) Look up knowhow at Dictionary.com
also know-how, "technical expertise," 1838, American English, from know (v.) + how.
knowing (adj.) Look up knowing at Dictionary.com
"with knowledge of truth," late 14c., from present participle of know (v.). Related: Knowingly.
knowingly (adv.) Look up knowingly at Dictionary.com
late 14c., from knowing + -ly (2).
knowledge (n.) Look up knowledge at Dictionary.com
early 12c., cnawlece "acknowledgment of a superior, honor, worship;" for first element see know. Second element obscure, perhaps from Scandinavian and cognate with the -lock "action, process," found in wedlock. Meaning "capacity for knowing, understanding; familiarity; fact of knowing" is late 14c. Sense of "an organized body of facts or teachings" is from c.1400, as is that of "sexual intercourse." Also a verb in Middle English, knoulechen "acknowledge" (c.1200), later "find out about; recognize," and "to have sexual intercourse with" (c.1300).
knowledgeable (adj.) Look up knowledgeable at Dictionary.com
also knowledgable, c.1600, "capable of being known, recognizable" (a sense now obsolete), from knowledge in its Middle English verbal sense + -able. The modern sense of "having knowledge, displaying knowledge" is from 1829 and probably a new formation.
known Look up known at Dictionary.com
past participle of know.
knub (n.) Look up knub at Dictionary.com
"small lump," 1560s, probably cognate with Low German knubbe "knot, knob," Danish knub "block, log, stump" (see knob).
knuckle (n.) Look up knuckle at Dictionary.com
mid-14c., knokel "finger joint; any joint of the body, especially a knobby one; morbid lump or swelling;" common Germanic (cognates: Middle Low German knökel, Middle Dutch cnockel, German knöchel), literally "little bone," a diminutive of Proto-Germanic root *knuck- "bone" (compare German Knochen "bone).

As a verb from 1740, originally in the game of marbles. To knuckle down "apply oneself earnestly" is 1864 in American English, extended from marbles (putting a knuckle on the ground in assuming the hand position preliminary to shooting); 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." The face-busting knuckle-duster is from 1858 (a duster was a type of protective coat worn by workmen).
knuckleball (n.) Look up knuckleball at Dictionary.com
also knuckle-ball, baseball pitch, by 1909, from knuckle (n.) + ball (n.1). So called from the position of the fingers in throwing it. Related: Knuckleballer.
knucklehead (n.) Look up knucklehead at Dictionary.com
"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.) Look up knurl at Dictionary.com
"hard excrescence," c.1600, probably a diminutive of Middle English knor "knot" (c.1400), related to gnarl, from Proto-Germanic *knur- (cognates: German knorren "a knotty excrescence"). Related: Knurly.
koala (n.) Look up koala at Dictionary.com
Australian marsupial, 1808, from the Aboriginal name of the animal, variously given as koola, kulla, kula.
koan (n.) Look up koan at Dictionary.com
Zen paradox, 1946, from Japanese ko "public" + an "matter for thought."
Kobe Look up Kobe at Dictionary.com
type of fine beef, named for the region in Japan where it is raised, from Japanese ko "god" + he "house."
Kodak Look up Kodak at Dictionary.com
brand of 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. Kodachrome, registered trademark for a method of color photography, 1915; the product was discontinued in 2006.
Kodiak Look up Kodiak at Dictionary.com
Alaskan island, from Russian Kadiak, from Alutiiq (Eskimo) qikertaq "island."
Koh-i-noor (n.) Look up Koh-i-noor at Dictionary.com
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.) Look up kohl at Dictionary.com
"powder used to darken eyelids," 1799, from Arabic kuhl (see alcohol).
kohlrabi (n.) Look up kohlrabi at Dictionary.com
also kohl-rabi, kohl rabi, kind of cabbage, 1807, from German Kohlrabi (16c.), from Italian cavoli rape, plural of cavolo rapo "cole-rape;" see cole + rape (n.2). Form influenced in German by German kohl "cabbage."
koi (n.) Look up koi at Dictionary.com
1727, from a Japanese local name for "carp."
koine (n.) Look up koine at Dictionary.com
common literary dialect of Greek in Roman and early medieval period, 1903, from feminine singular of Greek koinos "common, ordinary" (see coeno-). Used earlier as a Greek word in English.
koinonia (n.) Look up koinonia at Dictionary.com
1865, Greek, literally "communion, fellowship," from koinos "common, ordinary" (see coeno-).
kola (n.) Look up kola at Dictionary.com
"the cola nut," 1830, variant of cola (q.v.).
kolkhoz (n.) Look up kolkhoz at Dictionary.com
U.S.S.R. collective farm, 1921, from Russian kolkhoz, contraction of kollektivnoe khozyaistvo "collective farm."
Komodo dragon (n.) Look up Komodo dragon at Dictionary.com
1927, named for Indonesian island of Komodo, where it lives.
Komsomol (n.) Look up Komsomol at Dictionary.com
Russian communist youth organization, 1934, from Russian Komsomol, contraction of Kommunisticheskii Soyuz Molodezhi "Communist Union of Youth."
kook (n.) Look up kook at Dictionary.com
1960, American English slang; see kooky.
kookaburra (n.) Look up kookaburra at Dictionary.com
1890, from a native Australian word.
kooky (adj.) Look up kooky at Dictionary.com
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.) Look up kop at Dictionary.com
"hill," 1835, from Afrikaans, from Dutch kop "head," from the Germanic form of the root of English cup (compare German Kopf "head").
kopeck (n.) Look up kopeck at Dictionary.com
1/100 of a ruble, from Russian kopeika, from kop'e "lance" (cognate with Greek kopis "chopper, cleaver;" see hatchet); so called because the coin showed the czar with lance in hand.
kopje (n.) Look up kopje at Dictionary.com
small hill in South Africa, from S.African Dutch, diminutive of Dutch kop "hill; head" (see kop).
Koran Look up Koran at Dictionary.com
1610s, from Arabic qur'an "a reading, recitation, book," from root of quara-a "he read, recited." Related: Koranic.
Kore Look up Kore at Dictionary.com
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).
Korea Look up Korea at Dictionary.com
from Chinese Gao li, name of a dynasty founded 918, literally "high serenity." Japanese Chosen is from Korean Choson, literally "land of morning calm," from cho "morning" + son "calm." Related: Korean (1610s).
kos (n.) Look up kos at Dictionary.com
measure of distance in India (about 2 miles), from Hindi kos, from Sanskrit krosah, literally "a call, a shout;" thus, "distance within which a man's shout can be heard."
kosher (adj.) Look up kosher at Dictionary.com
"ritually fit or pure" (especially of food), 1851, from Yiddish kosher, from Hebrew kasher "fit, proper, lawful," from base of kasher "was suitable, proper." Generalized sense of "correct, legitimate" is from 1896.
kowtow (n.) Look up kowtow at Dictionary.com
also kow-tow, 1804, from Chinese k'o-t'ou custom of touching the ground with the forehead to show respect or submission, literally "knock the head," from k'o "knock, bump" + t'ou "head." The verb in the figurative sense of "act in an obsequious manner" is from 1826. Related: Kowtowed; kowtowing.
kraal (n.) Look up kraal at Dictionary.com
"village, pen, enclosure," 1731, South African, from colonial Dutch kraal, from Portuguese curral (see corral).
kraken (n.) Look up kraken at Dictionary.com
monster of the North Sea, 1755, from Norwegian dialectal krake.
Krakow Look up Krakow at Dictionary.com
city in southern Poland, said to have been named for a supposed founder, Krak.
Kraut (n.) Look up Kraut at Dictionary.com
"a German" (especially a German soldier), 1841, but popularized during World War I, from German kraut "cabbage," considered a characteristic national dish.
Krebs cycle Look up Krebs cycle at Dictionary.com
1941, named for Sir Hans Adolf Krebs (1900-1981), German-born British biochemist.
Kremlin Look up Kremlin at Dictionary.com
1660s, Cremelena, from Old Russian kremlinu, later kremlin (1796), from kreml' "citadel, fortress," perhaps of Tartar origin. Originally the citadel of any Russian city, now especially the one in Moscow. Used metonymically for "government of the U.S.S.R." from 1933. The modern form of the word in English might be via French.