Online Etymology Dictionary

klutz (n.): 1967, American English, from Yiddish klots "clumsy person, blockhead," literally "block, lump," from Middle High German klotz "lump, ball." Compare German klotz "boor, clod," literally "wooden block" (see clot (n.)).
klutzy (adj.): 1965, from klutz + -y (2). Related: Klutziness.
kluxer (n.): contemptuous for "Klansman," 1879, American English; see Ku Klux Klan.
kn-: Middle English spelling of a common Germanic consonant-cluster (in Old English it was graphed as cn-; see K). The sound it represented persists in most of the sister languages, but in English it was reduced to "n-" in standard pronunciation by 1750, after about a century of weakening and fading. It was fully voiced in Old and Middle English.
knack (n.): mid-14c., "a deception, trick, device," a word of uncertain origin. Perhaps from or related to a Low German word meaning "a sharp sounding blow" (compare Middle English knak, late 14c.; German knacken "to crack;" also knap) and of imitative origin. Sense of "special skill" (in some specified activity) is first recorded 1580s, if this is in fact the same word. In old slang (mid-18c. to mid-19c.) nacky meant "full of knacks; ingenious, dexterous." For pronunciation, see kn-.
knacker (v.): "to kill, castrate" (1855), apparently from knacker (n.) "one who slaughters old or sick horses" (1812). This is probably the same word as the earlier knacker/nacker "harness-maker" (1570s), which survived in 18c. in dialects. The sense extension is perhaps because knackers supplied farmers general help with horse matters, including disposing of dead ones. The word is of uncertain origin, possibly from a dialectal survival of a Scandinavian word represented by Old Norse hnakkur "saddle," related to hnakki "back of the neck," and thus possibly related to neck (n.). Most often used in weakened sense of "to tire out" (1883) and usually encountered in its past tense, knackered.
knackered (adj.): "worn out, tired," 1883, past participle adjective from knacker (v.).
knap (v.): "to strike with a sharp sound," late 15c., echoic. Earlier (c. 1400) as a noun meaning "abrupt stroke." Especially "to chip or break by a sharp blow" (1530s), the sense shifting from the sound to the act that makes it. Especially of the method of sharpening flints from 1862. Related: Knapped; knapper; knapping. For pronunciation, see kn-.
knapsack (n.): c. 1600, from Low German Knapsack (16c.), probably from knappen "to eat" literally "to crack, snap" (imitative) + Sack "bag" (see sack (n.1)). Similar formation in Dutch knapzak.
knapweed (n.): so called for its knobby heads, from Middle English knap "ornamental knob; bunch or tuft; a button; knot or protuberance on a tree; joint in the stalk of a plant; testicle," from Old English cnæp "top, summit of a hill," or its cognate, Old Norse knappr "a knob, button, stud."
knave (n.): late Old English cnafa "boy, male child; male servant," from Proto-Germanic *knabon- (source also of Old High German knabo "boy, youth, servant," German knabe "boy, lad"); it is also probably related to Old English cnapa "boy, youth, servant," Old Norse knapi "servant boy," Dutch knaap "a youth, servant," Middle High German knappe "a young squire," German Knappe "squire, shield-bearer." Original sense unknown; Klein suggests the prehistoric meaning might have been "stick, piece of wood." For pronunciation, see kn-.

Sense of "rogue, rascal" is first recorded c. 1200, presumably via sense evolution from "a menial" to "one of low birth," and the low character supposed to be characteristic of such a condition. But through Middle English it kept also its non-pejorative meaning, as in knave-child (Scottish knave-bairn) "male child." In playing cards, "the jack," 1560s.
knavery (n.): "knavish deeds," 1520s, from knave + -ery.
knavish (adj.): late 14c., "low, vulgar," from knave + -ish. Meaning "rascally" is from late 15c. (implied in knavishly). Related: Knavishness.
knead (v.): Old English cnedan "to knead, manipulate by squeezing or pressing," from Proto-Germanic *knedan (source also of Old Saxon knedan, Middle Dutch cneden, Dutch kneden, Old High German knetan, German kneten, Old Norse knoða "to knead"). Originally a strong verb (past tense cnæd, past participle cneden). For pronunciation, see kn-. The evolution of the vowel is unusual. Related: Kneaded; kneading.
knee (n.): "joint between the principal bones of the leg," Old English cneo, cneow "knee," from Proto-Germanic *knewam (source also of Old Norse kne, Old Saxon kneo, Old Frisian kni, Middle Dutch cnie, Dutch knie, Old High German kniu, German Knie, Gothic kniu), from PIE root *genu- (1) "knee; angle" (source also of Sanskrit janu, Avestan znum, Hittite genu "knee;" Greek gony "knee," gonia "corner, angle;" Latin genu "knee"). For pronunciation, see kn-.

To be across (someone's) knee in reference to spanking is from 1866. Knee-breeches is from 1827; knee-pants is from 1858. Knee-slapper "funny joke" is from 1955.
knee (v.): early 13c., "to bend the knee, kneel," from Old English cneowian, from cneow (see knee (n.)). The meaning "to strike with the knee" is first recorded 1892. Related: Kneed; kneeing.
knee-deep (adj.): c. 1400, "up to the knees," from knee (n.) + deep (adj.).
knee-high (adj.): 1743, from knee (n.) + high (adj.). Phrase knee-high to a grasshopper first recorded 1851 (earliest form was knee-high to a toad, 1814).
knee-jerk (n.): patellar reflex, a neurological phenomenon discovered and named in 1876; see knee (n.) + jerk (n.1) in the medical sense. The figurative use appeared soon after the phrase was coined.
kneecap (n.): 1650s, "a covering or protection for the knee," from knee (n.) + cap (n.). Meaning "bone in front of the knee joint" is from 1869; the verb in the underworld sense of "to shoot (someone) in the knee" as punishment is attested by 1975. Related: Kneecapped.
kneel (v.): Old English cneowlian "to kneel, fall on the knees," from cneow (see knee (n.)). Similar formation in Middle Low German knelen, Middle Dutch cnielen, Dutch knielen Gothic knussjan. Past tense knelt is a modern formation (19c.) on analogy of feel/felt, etc. Related: Kneeler; kneeling.
kneepad (n.): also knee-pad, 1858, from knee (n.) + pad (n.).
knell (n.): Old English cnyll "sound made by a bell when struck or rung slowly," from knell (v.). Compare Dutch knal, German knall, Danish knald, Swedish knall. The Welsh cnull "death-bell" appears to be a borrowing from English. For vowel evolution, see bury. For pronunciation, see kn-.
knell (v.): Old English cnyllan "to toll a bell; strike, knock," cognate with Middle High German erknellen "to resound," Old Norse knylla "to beat, thrash;" probably imitative. Intransitive sense, in reference to a bell, is from late 14c. Related: Knelled; knelling.
knelt: past tense and past participle of kneel (v.).
Knesset: Israeli parliament, 1949, from Mishnaic Hebrew keneseth "gathering, assembly," from stem of Hebrew kanas "he gathered, assembled, collected."
knew: Old English cneow, past tense of know (v.).
knick-knack (n.): also knickknack, nicknack, "a pleasing trifle, toy," 1570s, a reduplication of knack (n.) "ingenious device, toy, trinket" (1530s), a specialized sense of knack (n.) "stratagem, trick."
Knickerbocker: "descendant of Dutch settlers of New York," 1831, from Diedrich Knickerbocker, the name under which Washington Irving published his popular "History of New York" (1809). The pen-name was borrowed from Irving's friend Herman Knickerbocker, and literally means "toy marble-baker," from German knicker, schoolboy slang for "marble," apparently an agent-noun from the imitative verb knikken "to snap."
knickers (n.): 1866, in reference to loose-fitting pants for men worn buckled or buttoned at the waist and knees, shortening of knickerbockers (1859), said to be so called for their resemblance to the trousers of old-time Dutchmen in Cruikshank's illustrations for Washington Irving's "History of New York" (see knickerbocker). As "short, loose-fitting undergarment for women," by 1882, now the usual sense.
knife (n.): "hand-held cutting instrument consisting of a short blade and handle," late Old English cnif, probably from Old Norse knifr "knife, dirk," from Proto-Germanic *knibaz (source also of Middle Low German knif, Middle Dutch cnijf, German kneif), a word of uncertain origin. To further confuse the etymology, there also are forms in -p-, such as Dutch knijp, German kneip. French canif "penknife" (mid-15c.) is borrowed from Middle English or Norse. For pronunciation, see kn-.
knife (v.): 1865, "stab or kill with a knife," from knife (n.). Intransitive meaning "move as a knife does" is from 1920. Related: Knifed; knifing.
knight (n.): Old English cniht "boy, youth; servant, attendant," a word common to the nearby Germanic languages (Old Frisian kniucht, Dutch knecht, Middle High German kneht "boy, youth, lad," German Knecht "servant, bondman, vassal"), of unknown origin. For pronunciation, see kn-. The plural in Middle English sometimes was knighten.

Meaning "military follower of a king or other superior" is from c. 1100. It began to be used in a specific military sense in the Hundred Years War, and gradually rose in importance until it became a rank in the nobility from 16c. Hence in modern British use, a social privilege or honorary dignity conferred by a sovereign as a reward, without regard for birth or deeds at arms. In 17c.-19c. a common jocularism was to call a craftsman or tradesman a knight of the and name some object associated with his work; e.g. knight of the brush for "painter." Knight in shining armor in figurative sense is from 1917, from the man who rescues the damsel in distress in romantic dramas (perhaps especially "Lohengrin"). For knight-errant, see errant.

The horse-headed chess piece so called from mid-15c. Knights of Columbus, society of Catholic men, founded 1882 in New Haven, Connecticut, U.S.; Knights of Labor, trade union association, founded in Philadelphia, 1869; Knights of Pythias, secret order, founded in Washington, 1864.
knight (v.): "to make a knight of (someone), to dub or create a knight," early 13c., from knight (n.). Related: Knighted; knighting.
knighthood (n.): Old English cnihthad "the period between childhood and manhood;" see knight (n.) + -hood. Sense of "rank or dignity of a knight" is from c. 1300, and probably is an independent formation.
knightly (adj.): Old English cnihtlic "boyish, childish;" see knight (n.) + -ly (1). Meaning "chivalrous, befitting a knight" is from late 14c.
knish (n.): 1930, from Yiddish, from Russian knysh, a kind of cake.
knit (v.): Old English cnyttan "to tie with a knot, bind together, fasten by tying," related to Old Norse knytja "bind together, form into a knot," Middle Low German knütten "to tie, knot," Old English cnotta "a knot," from Proto-Germanic *knuttjan, from stem *knutt-. Of brows, late 14c. Intransitive meaning "do knitting, weave by looping or knotting a continuous thread" (especially in reference to plain stitch) is from 1520s. Intransitive meaning "become compact or consolidated" is from c. 1600. Related: Knitted; knitting. For pronunciation, see kn-.
knitter (n.): mid-15c., "that which ties or knits" in any sense, agent noun from knit (v.). Meaning "one who does knitting work" is from 1510s (c. 1300 as a surname). Occasionally knitster (1640s).
knitting (n.): late 14c., "a fastening with a rope or thread;" mid-15c., "a joining or binding together," verbal noun from knit (v.). In Middle English also "unity; a bond, unifying force; interconnection; a relationship," but these are lost. Meaning "act of weaving a continuous thread by loops or knots" is from 1711. Meaning "knitted work, work done by a knitter" is from 1848. Knitting-needle is from 1590s.
knob (n.): late 14c., knobe, probably from a Scandinavian or German source (compare Middle Low German knobbe "knob," Middle Dutch cnoppe, Dutch knop, Old Frisian knopp, knapp, Old High German knopf, German Knopf "button," Old Norse knyfill "short horn"). Meaning "knoll, isolated round hill" is first recorded 1640s, especially in U.S. For pronunciation, see kn-.
knobby (adj.): 1540s, from knob + -y (2). Alternative form knobbly attested from 1859. Related: Knobbiness.
knock (v.): Old English cnocian (West Saxon cnucian), "to pound, beat; knock (on a door)," likely of imitative origin. Figurative meaning "deprecate, put down" is from 1892. Related: Knocked; knocking. Of engines from 1869. To knock back (a drink) "swallow quickly or at a gulp" is from 1931. Many phrases are in reference to the auctioneer's hammer, for example knock down (v.) "dispose of (something) at auction" (1760).
knock (n.): mid-14c., from knock (v.). As an engine noise, from 1899.
knock up (v.): 1660s, "arouse by knocking at the door," from knock (v.) + up (adv.). However it is little used in this sense in American English, where the phrase means "get a woman pregnant" (1813), possibly ultimately from knock in a sense "to copulate with" (1590s; compare slang knocking-shop "brothel," 1860).
Knocked up in the United States, amongst females, the phrase is equivalent to being enciente, so that Englishmen often unconsciously commit themselves when amongst our Yankee cousins. [John Camden Hotten, "The Slang Dictionary," London, 1860]
knock-down (adj.): also knockdown, 1680s, from the verbal phrase knock down, attested from mid-15c. in the sense "fell to the ground;" see knock (v.) + down (adv.). As a noun from 1809. Phrase knock-down, drag-out is from 1827.
knock-kneed (adj.): 1774, from knock (v.) + knee (n.).
knockabout (adj.): also knock-about, "suitable for anything," 1876, from verbal phrase knock about (intrans.) "wander here and there" (1833; knock around in the same sense is from 1848); see knock (v.) + around (adv.).
knocker (n.): late 14c., agent noun from knock (v.). Sense of "door banger" is by 1590s. Knockers "a woman's breasts" is slang attested from 1941.
knockoff (n.): also knock-off, "cheap imitation," 1966, from the verbal phrase knock off "do hastily" (1817), in reference to the casual way the things are made. The verbal phrase knock off is attested from 1640s as "desist, stop" (work, study, etc.), hence knockoff (n.) "act of leaving work" (1899) and, probably, the command knock it off "stop it" (1880), which was perhaps reinforced by the auctioneer's use of the term for "dispose of quickly." To knock (someone) off in the underworld slang sense of "kill, murder" is from 1919. See knock (v.) + off (adv.).